When you take the Attack action and attack with only a glaive, halberd, quarterstaff, or spear, you can use a bonus action to make a melee attack with the opposite end of the weapon. This attack uses the same ability modifier as the primary attack. The weapon’s damage die for this attack is a d4, and it deals bludgeoning damage.
While you are wielding a glaive, halberd, pike, quarterstaff, or spear, other creatures provoke an opportunity attack from you when they enter your reach.
You have advantage on Constitution saving throws that you make to maintain your concentration on a spell when you take damage.
You can perform the somatic components of spells even when you have weapons or a shield in one or both hands.
When a hostile creature's movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature.
When you cast a spell that requires you to make an attack roll, the spell's range is doubled.
Your ranged spell attacks ignore half cover and three-quarters cover.
You learn one cantrip that requires an attack roll. Choose the cantrip from the wizard spell list. Your spellcasting ability for this cantrip is Intelligence.
On your turn, when you score a critical hit with a melee weapon or reduce a creature to 0 hit points with one, you can make one melee weapon attack as a bonus action.
Before you make a melee attack with a heavy weapon that you are proficient with, you can choose to take a -5 penalty to the attack roll. If the attack hits, you add +10 to the attack's damage.
Bugbear Trait
Long-Limbed.When you make a melee attack on your turn, your reach for it is 5 feet greater than normal.
Discussion pertains to OA, Reach, and its interactions.
Spell Sniper Booming Blade range up to 10'
Base no-Reach BugBear(Long-Limbed) OA Occurs 10'--->15' == 15'--->10' Should Always have this as Unarmed Strikes can be used by everyone even while wielding 2 handed weapon
Can be used for Spell Sniper Booming Blade through Warcaster
When a hostile creature's movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature.
Spell Sniper Booming Blade using Reach weapon is allowed as I am casting at this point.
Reach Weapon BugBear(Long-Limbed) OA Occurs 15'--->20' == 20'--->15'
Can't Not be used for Spell Sniper Booming Blade through Warcaster
The Question " Is 5'--->10' a Deadzone for OA while using a Bugbear
Base no-Reach BugBear(non Long-Limbed) OA Occurs 5'--->10' == 10'--->5' Should Always have this as Unarmed Strikes can be used by everyone even while wielding 2 handed weapon
Can be used for Spell Sniper Booming Blade through Warcaster
Reach Weapon BugBear(non Long-Limbed) OA Occurs 10'--->15' == 15'--->10'
Can be used for Spell Sniper Booming Blade through Warcaster
Cool Ty. I was really worried about the dead zone @ close range. Less range but better coverage
Keep in mind that Long-Limbed only works on your turn and therefore doesn't apply to AoO, just as stormknight mentioned above.
Therefore, the AoO range is only dependent on your weapon. If you are using a reach weapon, that would be the 15'/10' zone in either direction. Once they are in that range, they can move around at will without provoking an AoO as long as they don't leave it. So the 10' to 5' or any movement along the 10' or 5' range would be an AoO deadzone, just as movement along the 5' range wouldn't provoke AoO for non reach weapons.
I think this is part of the reason why long limbed only works on your turn. That deadzone would permanently be 10' or in and possibly 15' and in with a reach weapon otherwise.
Additionally, you can't use unarmed strikes for the AoO if you are using warcaster to cast booming blade since booming blade requires a melee weapon attack.
Edit to acknowledge stormknight pointing out long-limbed only working on the bugbear's turn and to point out that unarmed strikes can't be part of booming blade.
Keep in mind that Long-Limbed only works on your turn and therefore doesn't apply to AoO.
Therefore, the AoO range is only dependent on your weapon. If you are using a reach weapon, that would be the 15'/10' zone in either direction. Once they are in that range, they can move around at will without provoking an AoO as long as they don't leave it. So the 10' to 5' or any movement along the 10' or 5' range would be an AoO deadzone, just as movement along the 5' range wouldn't provoke AoO for non reach weapons.
I think this is part of the reason why long limbed only works on your turn. That deadzone would permanently be 10' or in and possibly 15' and in with a reach weapon otherwise.
Why can i not get a AoO with Unarmed Strikes 5'-->10' == 10'-->5'
I haven't looked into unarmed strikes with AoO while carrying a two handed weapon. My immediate take is that you wouldn't want to use your reaction to deal 1 point of damage with a normal unarmed strike. As I mentioned in an edit previously, the unarmed strike can't be used for booming blade per the casting requirements of booming blade. If you wanted to use something like shocking grasp for the 5' version, I might be inclined to consider it until I had better researched the issue.
If you're using a Polearm weapon they are generally 2 handed and so you won't have a free hand to make an AoO unarmed. (I think)
You can. Two-handed weapons only require two hands to attack with them; you can carry them in one hand, and leave the other free for things like spellcasting and object interactions. Moreover, unarmed attacks can be made with body parts other than hands: headbutts, kicks, elbow strikes are all Unarmed Attacks.
I could see an instance where a polearm could be grasped one handed by the off-hand to make a punch similar to being able to cast spells with somatic or material components with a 2 hand weapon without having to stow the weapon. I'm just doubting the wisdom behind using your reaction to do so without the ability to do more than 1 point of damage or no other way to use your reaction.
I think that the OP is trying to make a case for using the unarmed strike to cast booming blade as part of the AoO using warcaster. My thought is that if you are trying to use something that wouldn't normally trigger an AoO as part of the AoO, it shouldn't be used. I used shocking grasp as an example earlier, but I think I might have to reconsider that due to spell sniper. Perhaps toll the dead.
Edit acknowledge Tonio getting in on the free hand bit first and adding my thoughts on what I think OP is trying to accomplish.
I could see an instance where a polearm could be grasped one handed by the off-hand to make a punch similar to being able to cast spells with somatic or material components with a 2 hand weapon without having to stow the weapon. I'm just doubting the wisdom behind using your reaction to do so without the ability to do more than 1 point of damage or no other way to use your reaction.
I think that the OP is trying to make a case for using the unarmed strike to cast booming blade as part of the AoO using warcaster. My thought is that if you are trying to use something that wouldn't normally trigger an AoO as part of the AoO, it shouldn't be used. I used shocking grasp as an example earlier, but I think I might have to reconsider that due to spell sniper. Perhaps toll the dead.
Edit acknowledge Tonio getting in on the free hand bit first and adding my thoughts on what I think OP is trying to accomplish.
When a hostile creature's movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature.
Rather Than making an opportunity attack I cast a spell. @ 5'-->10' === 10'-->5' Creatures are within my reach with reach weapon. Nowhere does it say i must use the unarmed strike because it proc'd the AoO. Rather Than AoO, Cast a spell(any spell, Single target, 1 Action) this spell just so happens to require melee weapon attack.
Correct me if I am wrong, but isn’t there something about unarmed strikes not being a weapon attack?
AoO: You can make an opportunity attack when a hostile creature that you can see moves out of your reach. To make the opportunity attack, you use your reaction to make one melee attack against the provoking creature. The attack occurs right before the creature leaves your reach.
Where did say i would use Unarmed Strike with Booming Blade. Nowhere in anything i wrote did i say that.
Question 1: Does player get AoO from Unarmed Strike 5' Reach while holding 2 Handed weapon? YES
I could see an instance where a polearm could be grasped one handed by the off-hand to make a punch similar to being able to cast spells with somatic or material components with a 2 hand weapon without having to stow the weapon. I'm just doubting the wisdom behind using your reaction to do so without the ability to do more than 1 point of damage or no other way to use your reaction.
Whether it's a good idea or not is not really the issue we're discussing, but I can think of at least one situation where someone might want to do that: the Sentinel Feat. A creature with the Sentinel Feat might prefer to stop the target from moving away, and therefore use their opportunity attack just as the target is about to leave their 5' unarmed range, to drop their speed to 0 and prevent them from leaving their 5' range, even if that means losing 4.725 average damage (assuming 1+str unarmed damage, and 1d10+str reach weapon damage). They could forgo their unarmed OA and elect to take their reach weapon OA, dealing more damage, and stopping the target at 10' rather than 5', but they might have a reason to prefer the target at 5' rather than 10'.
Of course, if they have the option of using Booming Blade (via War Caster), the point is academic; they won't be losing any damage by taking their unarmed OA, choosing to use Booming Blade for their attack, and casting that using their reach weapon.
Right, Joellee053 is saying that they would use the unarmed strike to proc the option for an AoO. Then in lieu of using the AoO, they would invoke the warcaster clause to cast a spell. For this spell, they would choose to cast booming blade, which requires a weapon attack to cast. When coupled with polearm master and a reach weapon, the character who have the opportunity to use their reaction to attack when a creature moves from 15' to 10' (PAM), in addition to moving from 10' to 15' (reach weapon) and 5' to 10' (normal AoO, using unarmed strike as the trigger). OP intent is to use warcaster to replace all of those AoOs with booming blade to maximize damage (using spell sniper to increase the range of booming blade when needed).
On the one hand, that's a lot of AoO triggers. On the other, that's a lot of resources used (3 ASIs for a bugbear meaning level 8 at the soonest with fighter 8, level 10 with fighter 6/X 4, or level 12) to be able to do it and it's only possible once per round. It does feel a little dirty to me having the full weapon damage (plus the spell damage and potential rider) both the 10' and the 5' AoO, but I can't think of a reason RAW that it shouldn't work. I might be inclined to limit the 5' ones that triggered by unarmed strikes to just spell damage spells (ie not booming blade and green flame blade) in my games just because it doesn't feel right without an official ruling, but I wouldn't make a fuss about it if another DM ruled in favor of it.
Sentinel would be an excellent example of foregoing damage in favor of unarmed strike.
In light of the points that Joelle053 brought up with the reaches and AoOs, I do think that the only thing stopping the combo would be DM ruling. It does still feel a little dirty, but I'd allow it in most of my settings.
Bugbear doesn't bring anything to the table, though, since their reach only applies on their turn. Even if the OA were triggered on their Turn (say, the Bugbear is also a Bard or GOOlock, and cast Dissonant Whispers to make the target run away and trigger the OA), they only have the extra Reach when they make a melee attack, and they haven't, yet. Well, maybe if they multiclass Fighter, and use Action Surge... 1) regular Action, use Attack to attack in melee, granting Reach for the entire Turn, 2) Action Surge, use Action to cast Dissonant Whispers, target fails Saving Throw, and runs away, 3) use Reaction for OA when target leaves the 15' reach. In that case, even with War Caster and Spell Sniper, Booming Blade couldn't be used, since its range is 5', doubled to 10' with Spell Sniper, so 15' would be out of range. In fact, in that case (regular action attack, action surge Dissonant Whispers), an OA could only be taken as the target leaves the 10' reach of Unarmed, or the 15' reach of a reach weapon: there is no 5' reach to exit in this case, since the Bugbear has +5' reach for the turn, and there is no 0' reach attack to extend to 5' by Long Limbed. So without Spell Sniper, Booming Bladecannot be used for an OA if the Bugbear already melee attacked that Turn.
This is a very interesting situation to me. I love the SCAG cantrips, and I find builds that combo things like PAM & War Caster fascinating for battlefield control. I even agree with almost every point made so far.. except bootstrapping a full weapon BB off of an "unarmed" AoO (bear with me 'til the end).
I think you're extrapolating your final position based on things that Jeremy Crawford has not actually said. What Jeremy does say is:
Just because you have multiple "reaches" does not mean that an AoO provoked by one "reach" can be substituted for any of your other options. If you're two-handing a reach weapon, and a creature provokes an AoO from your "unarmed" range, you can't substitute that with your reach weapon at that range.
With War Caster, you can cast a single-target spell, instead of a melee opportunity attack, with the weapon & "range" that triggered it. If you are taking your reaction as a creature moves across the 5' line (in either direction; PAM), your options are restricted to things that trigger & resolve an AoO at that range & at that moment.
Booming Blade requires a melee weapon attack be made as the material component. Unarmed strikes do not qualify. Reach weapons do not qualify because they do not provoke attacks of opportunity at this range. You cannot substitute an AoO by casting Booming Blade with a reach weapon if the reach weapon does not provoke an AoO at that range. You can't start to stick out your foot to trip the fleeing guy (unarmed AoO; totally fine), decide to cast a spell instead (War Caster; still fine), and then channel that spell through an attack, with a different weapon, with a different reach. ALL conditions have to be met.
Are there ways around this? Absolutely! 1H weapon (5' reach) + whip (10' reach). Boom!
Are there ways around this while still using PAM? Absolutely! Spear or Quarterstaff (1H, 5' reach, PAM) + whip (10' reach). Bam!
Are there ways around this while still using a 2H Reach weapon and PAM? Nope.
Can all of this be rendered moot if unarmed attacks would qualify for SCAG cantrips? Absolutely! But they don't.
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This is a very interesting situation to me. I love the SCAG cantrips, and I find builds that combo things like PAM & War Caster fascinating for battlefield control. I even agree with almost every point made so far.. except bootstrapping a full weapon BB off of an "unarmed" AoO (bear with me 'til the end).
I think you're extrapolating your final position based on things that Jeremy Crawford has not actually said. What Jeremy does say is:
Just because you have multiple "reaches" does not mean that an AoO provoked by one "reach" can be substituted for any of your other options. If you're two-handing a reach weapon, and a creature provokes an AoO from your "unarmed" range, you can't substitute that with your reach weapon at that range.
With War Caster, you can cast a single-target spell, instead of a melee opportunity attack, with the weapon & "range" that triggered it. If you are taking your reaction as a creature moves across the 5' line (in either direction; PAM), your options are restricted to things that trigger & resolve an AoO at that range & at that moment.
Booming Blade requires a melee weapon attack be made as the material component. Unarmed strikes do not qualify. Reach weapons do not qualify because they do not provoke attacks of opportunity at this range. You cannot substitute an AoO by casting Booming Blade with a reach weapon if the reach weapon does not provoke an AoO at that range. You can't start to stick out your foot to trip the fleeing guy (unarmed AoO; totally fine), decide to cast a spell instead (War Caster; still fine), and then channel that spell through an attack, with a different weapon, with a different reach. ALL conditions have to be met.
Are there ways around this? Absolutely! 1H weapon (5' reach) + whip (10' reach). Boom!
Are there ways around this while still using PAM? Absolutely! Spear or Quarterstaff (1H, 5' reach, PAM) + whip (10' reach). Bam!
Are there ways around this while still using a 2H Reach weapon and PAM? Nope.
Can all of this be rendered moot if unarmed attacks would qualify for SCAG cantrips? Absolutely! But they don't.
This is the basis for why it feels a little dirty to me. What complicates the issue is that there is nothing that prevents a spell being cast at any range that is within its range (ie just because a spell has a range of 60' doesn't mean it has to be cast at 60'). Thus, just because spell sniper gives booming blade a range of 10', it doesn't require that the spell be cast at 10'. The trigger for an AoO isn't that you stuck your blade out to hit someone, but the fact that you can as they are leaving your reach. Warcaster gives you the chance to make a spell attack in lieu of an attack of opportunity, as long as the spell can be used within that range and it only targets one creature. Part of the casting requirements for booming blade is the melee attack. There isn't anything preventing booming blade from being cast at 5' normally, and there isn't anything allowing it at reach without spell sniper. During a normal attack with spell sniper, there isn't anything preventing booming blade from being cast at either 5' or 10' with a reach weapon (perhaps disadvantage if it's with a lance and the character isn't mounted). Assuming that a DM would allow the AoO for the unarmed strike while the character is holding a reach weapon, I can't see a good reason why it shouldn't be allowed to interact with warcaster as the OP desires.
I think that this would have to be something that was brought up at zero session or fairly early and between sessions. This wouldn't be a nice trick to play on a DM in the moment.
The only reason why bugbear is relevant is because that's what the OP said the character was and the fact that it eliminates the human variant option for pushing up the timeframe for spell sniper/warcaster/PAM. Technically, PAM doesn't have to factor in for the majority of the conversation, since it's only affecting the incoming AoO availability and not the reach aspect.
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INFO
Bugbear Trait
Long-Limbed. When you make a melee attack on your turn, your reach for it is 5 feet greater than normal.
Discussion pertains to OA, Reach, and its interactions.
Spell Sniper Booming Blade range up to 10'
Base no-Reach BugBear(Long-Limbed) OA Occurs 10'--->15' == 15'--->10' Should Always have this as Unarmed Strikes can be used by everyone even while wielding 2 handed weapon
Can be used for Spell Sniper Booming Blade through Warcaster
When a hostile creature's movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature.
Spell Sniper Booming Blade using Reach weapon is allowed as I am casting at this point.
Reach Weapon BugBear(Long-Limbed) OA Occurs 15'--->20' == 20'--->15'
Can't Not be used for Spell Sniper Booming Blade through Warcaster
The Question " Is 5'--->10' a Deadzone for OA while using a Bugbear
Note that the Bugbear additional 5 ft. of reach is only for melee attacks made on their turn and therefore doesn't apply to Opportunity Attacks.
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Base no-Reach BugBear(non Long-Limbed) OA Occurs 5'--->10' == 10'--->5' Should Always have this as Unarmed Strikes can be used by everyone even while wielding 2 handed weapon
Can be used for Spell Sniper Booming Blade through Warcaster
Reach Weapon BugBear(non Long-Limbed) OA Occurs 10'--->15' == 15'--->10'
Can be used for Spell Sniper Booming Blade through Warcaster
Cool Ty. I was really worried about the dead zone @ close range. Less range but better coverage
Keep in mind that Long-Limbed only works on your turn and therefore doesn't apply to AoO, just as stormknight mentioned above.
Therefore, the AoO range is only dependent on your weapon. If you are using a reach weapon, that would be the 15'/10' zone in either direction. Once they are in that range, they can move around at will without provoking an AoO as long as they don't leave it. So the 10' to 5' or any movement along the 10' or 5' range would be an AoO deadzone, just as movement along the 5' range wouldn't provoke AoO for non reach weapons.
I think this is part of the reason why long limbed only works on your turn. That deadzone would permanently be 10' or in and possibly 15' and in with a reach weapon otherwise.
Additionally, you can't use unarmed strikes for the AoO if you are using warcaster to cast booming blade since booming blade requires a melee weapon attack.
Edit to acknowledge stormknight pointing out long-limbed only working on the bugbear's turn and to point out that unarmed strikes can't be part of booming blade.
Why can i not get a AoO with Unarmed Strikes 5'-->10' == 10'-->5'
I haven't looked into unarmed strikes with AoO while carrying a two handed weapon. My immediate take is that you wouldn't want to use your reaction to deal 1 point of damage with a normal unarmed strike. As I mentioned in an edit previously, the unarmed strike can't be used for booming blade per the casting requirements of booming blade. If you wanted to use something like shocking grasp for the 5' version, I might be inclined to consider it until I had better researched the issue.
If you're using a Polearm weapon they are generally 2 handed and so you won't have a free hand to make an AoO unarmed. (I think)
Mega Yahtzee Thread:
Highest 41: brocker2001 (#11,285).
Yahtzee of 2's: Emmber (#36,161).
Lowest 9: JoeltheWalrus (#312), Emmber (#12,505) and Dertinus (#20,953).
You can. Two-handed weapons only require two hands to attack with them; you can carry them in one hand, and leave the other free for things like spellcasting and object interactions. Moreover, unarmed attacks can be made with body parts other than hands: headbutts, kicks, elbow strikes are all Unarmed Attacks.
Yeah that's true. I always forget about that last part.
Mega Yahtzee Thread:
Highest 41: brocker2001 (#11,285).
Yahtzee of 2's: Emmber (#36,161).
Lowest 9: JoeltheWalrus (#312), Emmber (#12,505) and Dertinus (#20,953).
I could see an instance where a polearm could be grasped one handed by the off-hand to make a punch similar to being able to cast spells with somatic or material components with a 2 hand weapon without having to stow the weapon. I'm just doubting the wisdom behind using your reaction to do so without the ability to do more than 1 point of damage or no other way to use your reaction.
I think that the OP is trying to make a case for using the unarmed strike to cast booming blade as part of the AoO using warcaster. My thought is that if you are trying to use something that wouldn't normally trigger an AoO as part of the AoO, it shouldn't be used. I used shocking grasp as an example earlier, but I think I might have to reconsider that due to spell sniper. Perhaps toll the dead.
Edit acknowledge Tonio getting in on the free hand bit first and adding my thoughts on what I think OP is trying to accomplish.
Rather Than making an opportunity attack I cast a spell. @ 5'-->10' === 10'-->5' Creatures are within my reach with reach weapon. Nowhere does it say i must use the unarmed strike because it proc'd the AoO. Rather Than AoO, Cast a spell(any spell, Single target, 1 Action) this spell just so happens to require melee weapon attack.
Correct me if I am wrong, but isn’t there something about unarmed strikes not being a weapon?
AoO: You can make an opportunity attack when a hostile creature that you can see moves out of your reach. To make the opportunity attack, you use your reaction to make one melee attack against the provoking creature. The attack occurs right before the creature leaves your reach.
Where did say i would use Unarmed Strike with Booming Blade. Nowhere in anything i wrote did i say that.
Question 1: Does player get AoO from Unarmed Strike 5' Reach while holding 2 Handed weapon? YES
https://twitter.com/JeremyECrawford/status/725193622581293056
Question 2: Can that AoO be change to a spell? Yes , WarCaster / Same Target, Single Target, Any Spell with Casting 1 Action
Question 3: Is Booming Blade a Spell? Yes. Single Target, Casting of 1 Action
So a AoO Due to unarmed strike can be converted into a casting of Booming Blade due to Warcaster. Period.
https://twitter.com/quadhund/status/984156268469325824
Whether it's a good idea or not is not really the issue we're discussing, but I can think of at least one situation where someone might want to do that: the Sentinel Feat. A creature with the Sentinel Feat might prefer to stop the target from moving away, and therefore use their opportunity attack just as the target is about to leave their 5' unarmed range, to drop their speed to 0 and prevent them from leaving their 5' range, even if that means losing 4.725 average damage (assuming 1+str unarmed damage, and 1d10+str reach weapon damage). They could forgo their unarmed OA and elect to take their reach weapon OA, dealing more damage, and stopping the target at 10' rather than 5', but they might have a reason to prefer the target at 5' rather than 10'.
Of course, if they have the option of using Booming Blade (via War Caster), the point is academic; they won't be losing any damage by taking their unarmed OA, choosing to use Booming Blade for their attack, and casting that using their reach weapon.
Right, Joellee053 is saying that they would use the unarmed strike to proc the option for an AoO. Then in lieu of using the AoO, they would invoke the warcaster clause to cast a spell. For this spell, they would choose to cast booming blade, which requires a weapon attack to cast. When coupled with polearm master and a reach weapon, the character who have the opportunity to use their reaction to attack when a creature moves from 15' to 10' (PAM), in addition to moving from 10' to 15' (reach weapon) and 5' to 10' (normal AoO, using unarmed strike as the trigger). OP intent is to use warcaster to replace all of those AoOs with booming blade to maximize damage (using spell sniper to increase the range of booming blade when needed).
On the one hand, that's a lot of AoO triggers. On the other, that's a lot of resources used (3 ASIs for a bugbear meaning level 8 at the soonest with fighter 8, level 10 with fighter 6/X 4, or level 12) to be able to do it and it's only possible once per round. It does feel a little dirty to me having the full weapon damage (plus the spell damage and potential rider) both the 10' and the 5' AoO, but I can't think of a reason RAW that it shouldn't work. I might be inclined to limit the 5' ones that triggered by unarmed strikes to just spell damage spells (ie not booming blade and green flame blade) in my games just because it doesn't feel right without an official ruling, but I wouldn't make a fuss about it if another DM ruled in favor of it.
Sentinel would be an excellent example of foregoing damage in favor of unarmed strike.
In light of the points that Joelle053 brought up with the reaches and AoOs, I do think that the only thing stopping the combo would be DM ruling. It does still feel a little dirty, but I'd allow it in most of my settings.
Bugbear doesn't bring anything to the table, though, since their reach only applies on their turn. Even if the OA were triggered on their Turn (say, the Bugbear is also a Bard or GOOlock, and cast Dissonant Whispers to make the target run away and trigger the OA), they only have the extra Reach when they make a melee attack, and they haven't, yet. Well, maybe if they multiclass Fighter, and use Action Surge... 1) regular Action, use Attack to attack in melee, granting Reach for the entire Turn, 2) Action Surge, use Action to cast Dissonant Whispers, target fails Saving Throw, and runs away, 3) use Reaction for OA when target leaves the 15' reach. In that case, even with War Caster and Spell Sniper, Booming Blade couldn't be used, since its range is 5', doubled to 10' with Spell Sniper, so 15' would be out of range. In fact, in that case (regular action attack, action surge Dissonant Whispers), an OA could only be taken as the target leaves the 10' reach of Unarmed, or the 15' reach of a reach weapon: there is no 5' reach to exit in this case, since the Bugbear has +5' reach for the turn, and there is no 0' reach attack to extend to 5' by Long Limbed. So without Spell Sniper, Booming Blade cannot be used for an OA if the Bugbear already melee attacked that Turn.
This is a very interesting situation to me. I love the SCAG cantrips, and I find builds that combo things like PAM & War Caster fascinating for battlefield control. I even agree with almost every point made so far.. except bootstrapping a full weapon BB off of an "unarmed" AoO (bear with me 'til the end).
I think you're extrapolating your final position based on things that Jeremy Crawford has not actually said. What Jeremy does say is:
Just because you have multiple "reaches" does not mean that an AoO provoked by one "reach" can be substituted for any of your other options. If you're two-handing a reach weapon, and a creature provokes an AoO from your "unarmed" range, you can't substitute that with your reach weapon at that range.
With War Caster, you can cast a single-target spell, instead of a melee opportunity attack, with the weapon & "range" that triggered it. If you are taking your reaction as a creature moves across the 5' line (in either direction; PAM), your options are restricted to things that trigger & resolve an AoO at that range & at that moment.
Booming Blade requires a melee weapon attack be made as the material component. Unarmed strikes do not qualify. Reach weapons do not qualify because they do not provoke attacks of opportunity at this range. You cannot substitute an AoO by casting Booming Blade with a reach weapon if the reach weapon does not provoke an AoO at that range. You can't start to stick out your foot to trip the fleeing guy (unarmed AoO; totally fine), decide to cast a spell instead (War Caster; still fine), and then channel that spell through an attack, with a different weapon, with a different reach. ALL conditions have to be met.
Are there ways around this? Absolutely! 1H weapon (5' reach) + whip (10' reach). Boom!
Are there ways around this while still using PAM? Absolutely! Spear or Quarterstaff (1H, 5' reach, PAM) + whip (10' reach). Bam!
Are there ways around this while still using a 2H Reach weapon and PAM? Nope.
Can all of this be rendered moot if unarmed attacks would qualify for SCAG cantrips? Absolutely! But they don't.
You don't know what fear is until you've witnessed a drunk bird divebombing you while carrying a screaming Kobold throwing fire anywhere and everywhere.
This is the basis for why it feels a little dirty to me. What complicates the issue is that there is nothing that prevents a spell being cast at any range that is within its range (ie just because a spell has a range of 60' doesn't mean it has to be cast at 60'). Thus, just because spell sniper gives booming blade a range of 10', it doesn't require that the spell be cast at 10'. The trigger for an AoO isn't that you stuck your blade out to hit someone, but the fact that you can as they are leaving your reach. Warcaster gives you the chance to make a spell attack in lieu of an attack of opportunity, as long as the spell can be used within that range and it only targets one creature. Part of the casting requirements for booming blade is the melee attack. There isn't anything preventing booming blade from being cast at 5' normally, and there isn't anything allowing it at reach without spell sniper. During a normal attack with spell sniper, there isn't anything preventing booming blade from being cast at either 5' or 10' with a reach weapon (perhaps disadvantage if it's with a lance and the character isn't mounted). Assuming that a DM would allow the AoO for the unarmed strike while the character is holding a reach weapon, I can't see a good reason why it shouldn't be allowed to interact with warcaster as the OP desires.
I think that this would have to be something that was brought up at zero session or fairly early and between sessions. This wouldn't be a nice trick to play on a DM in the moment.
The only reason why bugbear is relevant is because that's what the OP said the character was and the fact that it eliminates the human variant option for pushing up the timeframe for spell sniper/warcaster/PAM. Technically, PAM doesn't have to factor in for the majority of the conversation, since it's only affecting the incoming AoO availability and not the reach aspect.