Reading the 4th edition version of the Allip, it had to ability to do permanent Wisdom drain.  That's pretty scary.  It's "babble" ability had the effect of a Hypnotism spell, which doesn't even exist in 5e.  Also, because it was incorporeal, its "attacks pass through armor."  Not sure how that part would have been incorporated into attack rolls...

The 5E version of the Allip instead does psychic damage.  The "babble" of 5e Allip can stun creatures for 1 round.  From this, it seems the 5e version is not both weaker and stronger than the 4E version.  

Trying to get some advice from a more experienced DM about balancing this monster to use against a 5th level party after considering both 4th edition and 5th edition versions.  Thoughts and suggestions appreciated.

A 5th level party of 4 players will kill the Allip in one round as its written.  Is this supposed to be a boss at the end of a long and hard fight or will your players take a long rest before they fight?  If they have been whittled down so they are very resource poor, like 80% of their spells/abilities used and they are at 50% health, the Allip is fine as written.  If he's the boss and you expect them to be at full health or close to it, they will one shot him in a round.

Example: Level 5 vengeance paladin 16 strength +1 sword makes two attacks:

Long Sword +1 w/ 16 strength: 1d8 + 4 = average damage 6 + level 2 smite on undead 4d8 = average damage 12 + hunters mark 1d= = average damage 3, total average damage = 21.  He'll have a 70% chance to hit at AC 13.  If he's dual wielding it would be highly likely the Paladin would one shot him in one round with smites.

Options:

1st) Turn Whispers of Madness and Howling Babble as a bonus action

2nd)  You can either increase the Allip's AC or HP's, because a typical level 5 party will wipe out a CR 5 monster very very quickly.  If they don't have magic weapons you can leave him as be but he'll be dead in 3 rds.

3rd) You could use his ability to walk through walls to make an attack and then move back through the wall to avoid being ganged up on.  Again though, the 40 hit points he's going to go down fast.

4th) You could make Howling Babble give an extra Bane effect for all of those who saved and it lasts for 10 rds.  Dispel Magic removes it.

5th) Have the Allip posses a creature and either try to join the party and betray them in the next combat encounter OR use the body to give the allip more hit points and some regular attacks, while he's in the corpse allow him to use Whispers of Madness and Howling Babble as a bonus action.  Reskin the Gnoll Packlord, his fleshy bits would make for a longer fight and when they take him down, out pops the Allip.

5e CR system is balanced on the 6-8 encounter adventuring day.  If you're running less than 6-8 encounters, or just throwing wooden dummy monsters at your party, encounter balance is way off. (See Also: The Adventuring Day) Second consideration is party size. Encounter balance works on the premise of 3-5 PCs per party. (See Also: Party Size) So, if you were to run your party of 4, 5th level characters through the ole Computron 4500, encounters work out as follows:

Your Allip comes in at a whopping 1,800 xp. So the encounter is already balanced. It will be an Easy or Medium combat encounter. 

Now... I'm going to assume (dangerous, I know..) that you would like this encounter to be more challenging to your party, and you'd be right to want to do that friend. So then, take a gander at Modifying Encounter Difficulty. Please note that the topics listed in that section are only a few suggestions on what can be done. Other suggestions might be to run your encounter in waves, increase the number and type of monster used and re-skinning a higher CR monster to narrate like an Allip but hit like a Dullahan. Or you can, as a last resort, smash two creatures together and come up with something that has never been seen before, that still narrates like an Allip.

A word of caution about things like permananent stat drain and level drain abilities: there's a reason that we don't have many abilities like that anymore. It absolutely sucks to play a character that has been permanantly mauled by stat drain. The game is supposed to be fun. Hard to see fun written in an encounter that removes 3-4 levels from your character and subsequently removes spell slots, attacks and abilities.

If you want a possibly different approach to running monsters, take a trip over to themonstersknow.com. Blog is penned by one Keith Ammann and gives some good insight on playing your beasties more optimally.

Anyway. Take care, have fun!

My thinking is that the point of this monster for my campaign is to weaken the party.  

How about these changes?

  *   Increase HD to 10d8+10 (so 55 hp). 

   *   Instead of a permanent WIS drain, it's attack does the listed amount of psychic damage (4d6+3) AND that person gets disadvantage on all concentration saving throws  and lose 2 points of WIS until a long rest?  Long rest recovers only 2 WIS points at a time, though.

   *  Change the range of Howling Babble to 50 feet.  Make it a bonus action recharging every 3 rounds.  Instead of being stunned, those who fail a WIS saving throw become affected as if under a Confusion spell (but without the Allip needing to concentrate).  Change the damage from 2d8+3 to 2d4+4 psychic.  

   *  Change Whispers of Madness so that anyone trying to use a mind-affecting ability (including trying to inflict psychic damage) on the Allip is Stunned for 1d4 rounds or until she succeeds on a CON saving throw.

   I would probably use it after the party gets attacked by a larger group of NPCs, and add some terrain hazards like quicksand or pits to spread the party out and make normal mobility difficult.  Add to that the Allip's move-through-solid objects feature, and I should be able to ambush and hit a spell-caster or two before the Allip goes down, right?

Maybe I'm reading into this, and if I am, I apologize in advance.

It seems like you're trying to square up a spellcaster with a high Wis. Your monster's main attack rider would really only effect spell casters that frequently rely on concentration spells and have a spell save dependent upon a Wisdom score (looking at you Spirit Guardians and Call Lightning).

Additionally, dropping the PCs Wis score with an attack, then hitting them with a Wis Save as a Bonus Action or be Confused is a quick way to a TPK. You're lowering their ability to pass the save DC and removing a majority of their action economy until the end of their next turn. Confusion is limited to 10 ft., while your ability will reach 50 ft. What this means is the spell will only target 2, maybe 3 creatures. Your ability could hit 3 times that amount, in the right circumstance. Without running a ton of mock encounters to test it for balance, I would suggest that your party will be circling the drain in a couple of rounds without the luck of an initiative roll and some strong magic items.

Lastly, I'm not sure that the practice of weakening an entire party without handing them a way to resolve these setbacks or at the very least forewarn them of "what happened to the last party that faced this monster" will be well received. Frankly, it sounds like an adversarial move. I could see haunting a PC with a Night Hag and allowing them to quest or research a way to rid oneself of a fiend. And to be certain, I'm all for lethal encounters. I frequently build things that my players feel that they have very small chance of success against. As a DM, we can easily kill a PC. That's not even a challenge. Make them feel like they're going to die, but manage to just win and they feel like heroes.

All that to say: If you're comfortable with running your creation and you think your players will enjoy it, completely ignore anything I've said and go with what you got. We're here to run fun games. If you and your players have fun, that's all that matters.

Edit: just read the last line of your post. The one about trying to hit a spell-caster or two... Really feels adversarial when I actually read the whole thing.

Quote from Kaavel >>

Maybe I'm reading into this, and if I am, I apologize in advance.

It seems like you're trying to square up a spellcaster with a high Wis. Your monster's main attack rider would really only effect spell casters that frequently rely on concentration spells and have a spell save dependent upon a Wisdom score (looking at you Spirit Guardians and Call Lightning).

Additionally, dropping the PCs Wis score with an attack, then hitting them with a Wis Save as a Bonus Action or be Confused is a quick way to a TPK. You're lowering their ability to pass the save DC and removing a majority of their action economy until the end of their next turn. Confusion is limited to 10 ft., while your ability will reach 50 ft. What this means is the spell will only target 2, maybe 3 creatures. Your ability could hit 3 times that amount, in the right circumstance. Without running a ton of mock encounters to test it for balance, I would suggest that your party will be circling the drain in a couple of rounds without the luck of an initiative roll and some strong magic items.

Lastly, I'm not sure that the practice of weakening an entire party without handing them a way to resolve these setbacks or at the very least forewarn them of "what happened to the last party that faced this monster" will be well received. Frankly, it sounds like an adversarial move. I could see haunting a PC with a Night Hag and allowing them to quest or research a way to rid oneself of a fiend. And to be certain, I'm all for lethal encounters. I frequently build things that my players feel that they have very small chance of success against. As a DM, we can easily kill a PC. That's not even a challenge. Make them feel like they're going to die, but manage to just win and they feel like heroes.

All that to say: If you're comfortable with running your creation and you think your players will enjoy it, completely ignore anything I've said and go with what you got. We're here to run fun games. If you and your players have fun, that's all that matters.

Edit: just read the last line of your post. The one about trying to hit a spell-caster or two... Really feels adversarial when I actually read the whole thing.

    No offense taken.  

    I'm trying to build an interesting set of encounters.  I know that most of the players are quite experienced, so I want to throw an unconventional monster at them.  I'm not going for a TPK, but I am trying to scare them a little.  Portential said that the original Allip is basically Easy mode for a party of level 5 PCs who number 3 to 5 players.  Heck, even 1 Paladin or a Sharpshooter Rogue w a magic bow could probably one-shot the original Allip.  So I'm proposing ways to raise the challenge without just adding a ton of HD and increasing with damage die, neither of which make the monster particularly interesting.  

    I believe the 4e Allip's ability actually extended to 60 feet and it's effect was equivalent to a Hypnotism spell that lasted 2d4 rounds.  And it had PERMANENT Wisdom drain.  What I'm proposing is actually a bit weaker than that (except I increased the HD).  So if I adjust down the HD to 6d8+6 (33 hit points), and make the Howling Babble effect last only 1d4+1 rounds would that be more reasonable?  

I read what Portential said, and conccur that a single Allip against 4 level 5 PCs, *as the only encounter of the adventuring day* will be a cakewalk. Agreed that making something more lethal doesn't make it more interesting neither does turning it into a sack of HP.  For your one monster to be a challenge of any sort (just my opinion here) it would need to be about CR 8 with Legendary tendencies to balance out the action economy. 

 Monster movement and the ability to use the battlefield for it's purposes are what might make this a challenge. Adding in environmental hazards that will slow and hinder PCs might allow the monster to choose it's targets without fear of too much reprisal. I would also suggest a light hand on the first round if there are a pile of failed saves and several stunned PCs. If this thing lands a crit for an average of 31(max roll 51) psychic damage, there might be a PC leaving horizontal.

Comparing 2e and 4e monster abilities to 5e monster abilities, done in a vaccum, is fine.  This isn't a vaccum. If you were to bring 2e and 4e creatures directly into 5e, there is no balance there. There's barely a comparison to be made. The AC scales are different, the HD scales are different, the to-hit mechanics are different... the list continues. If it helps, there is a document to convert from older editions to 5e found here. I found it to be an insightful read.

Thank you to you both.  

Looking at the conversion document, it doesn't say anything about 4E.  Do you think 4E is more like 2E?  

Quote from Song_of_Blues >>

Thank you to you both.  

Looking at the conversion document, it doesn't say anything about 4E.  Do you think 4E is more like 2E?  

 

 

 I read the conversion document , what WotC put out is weak sauce.  You can use the AC and the Movement from 2E to 5E, but the rest you should go to the DMG and use the build a monster suggestions there, and understand its fairly weakly written as well.  You'll have to balance it out.  I would suggest using 3E/3.5E monster manuals when possible for monster conversions to 5E, its a lot easier, add some more hp's and lower the AC and they come out very close.

Hmmmm, don't have a 3 or 3.5 E Monster Manual.  But I do have Volo's Guide to Monsters here on DDB.  Does that help at all?

Also, I noticed some text in the 4E version of the Allip that says "50% chance to ignore damage from a corporeal source."  That's defintely absent in the 5E version.  I'm assuming that means it includes magic weapons, right?  So that would roughly double the effective hit points...  

Check out the DM's guild sometime, try the 3.5 Monster Manual if you want to try some of the monsters from there for 5E for ideas.  I never played 4E, but I've looked at 4E manuals and the conversion to 5E is just jacked to get them to work, probably the hardest to convert state wise.  It was a really different game from the other versions of D&D.

I think I'll change Damage Resistance to include damage from slashing, bludgeoning, and piercing from non-Radiant magical weapons.  So only Radiant magic weapons damage do full damage to reflect that it is an Undead Incorporeal creature.  

Keep AC at 13 and increase HD to 12d8.

Howling Babble:  save DC change to 13.  Only does 2d4+3 damage.  Recharge on a 6.  

Have it mindlessly attack a PC next to a wall of the dungeon.  If the PC effectively retaliates (does more than 8 points of damage), the Allip retreats into the wall and tries to attack a different PC next a wall.  So it wouldn't specifically be targeting spellcasters.

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A note on damage resistances. You do have the ability to make creatures vulnerable to damage types as well as making them resistant. Stacking up resistances to a majority of damage types and not against a specific type (in this case Radiant) will give the perspective effectiveness of that damage type being more effective against the creature. You can achieve the same result by just making the creature vulnerable to that type of damage. Or, you can make them vulerable to one type and resistant to all others to make the difference in effect even more pronounced.

As to the conversion from 4e to 5e, I might suggest that there wouldn't be a need to convert as there should be a new stat block for the monster that you're looking for. Effectively, converting 4e monsters to 5e is like fixing the engine on your bicycle. You shouldn't find a need to create a new monster from 4e as most, if not all, of the monsters from 4e are already in 5e. If you absolutly need the different variants to match up specifically, I might suggest that sticking with the 4e ruleset might serve your DMing style better than switching to 5e.

Using monsters, as written, directly from the MM, VGtM or MToF is fine and good and will get you close enough to the probability that you design your encounter to meet. In my mind, stat blocks are not there as a constraint for your customization to stop at, they are meant to further serve the DM as a template, or a modular ability system to suit the DM's purpose. The same might be said about the vagueness and wishy-washy wording used in the cannonical sourcebooks. I don't find it difficult to make rulings or customize monsters or decide what spells an NPC spellcaster uses because of the weakly written and often cited poor game design. Instead, I see this as an opportunity for the DM to create something unique and styled towards their own world, their own table, their own players. YMMV.