Syluné’s Viper

Quote from Runenstahl >>

I am pretty sure this spell will be officially "rebalanced" soon. Until then, I will propose to my groups to change it. Intead of requiring a hit on an attack roll to work, now the target will have to fail a constitution check for the spell to work. It's a simple fix that changes as little as possible but allows legendary creatures to use their saves to withstand this spell.

IDK how often WOTC does errata, but this is for sure on the list. Especially since they errata'd Conjure Minor Elementals already. And I think your change is way better than the official. Still strong, but it wont take a Legendary creature out of a fight round 1. 

how to beat selunes viper, have 2 enemies instead of 1. both can cast an aoe spell lets say fireball, average damage 28, your wizard or druid passes the save but are now basicly out of temp hp anyway, or you roll slightly better than average and the temp hp is gone even with a passed save. The player got to use their ability and feel good about it but it didnt break anything since you choose to have more than 1 person in the fight. 
the other solution is to have more encounters per day. every spell is amazing if im only needing to fight 1 encounter per day and always have all my spellslots

Quote from Isaragnor >>

how to beat selunes viper, have 2 enemies instead of 1. both can cast an aoe spell lets say fireball, average damage 28, your wizard or druid passes the save but are now basicly out of temp hp anyway, or you roll slightly better than average and the temp hp is gone even with a passed save. The player got to use their ability and feel good about it but it didnt break anything since you choose to have more than 1 person in the fight. 
the other solution is to have more encounters per day. every spell is amazing if im only needing to fight 1 encounter per day and always have all my spellslots

How 2 beat ur scenario:

- Fireball meet counterspell. The SV caster is more than 60 feet away? The other caster with counter spell is also nearby. 

- Fire damage = the most commonly resisted damage next to Poison. Also absorb elements.

- Ran out of temp hp? Dang. Anyway, I cast SV again.

-Also, that mob lost an entire turn regardless since the spell says "While Poisoned, the target has the Incapacitated condition." No concentration so that mob loses a turn no matter what outside being able to move. 

-Even if I had no 3rd or higher slots left, I spent a turn removing the enemy from doing anything which is 100% worthwhile. Means the bad guy couldnt do anything and my party got to beat on the bad guy for free while the mobs focused someone running away. GG EZ! 

My point is, that there is no other spell or effect that takes a target out of the fight that does NOT allow a saving throw (and therefore a legendary save for a boss). That is what makes this spell too powerful in my opinion.

You can use your turn to cast this 3rd level spell and make an attack. If it hits (and there are many ways to get advantage and other bonusses to help you with that) the target creature looses a turn. It really doesn't matter that the enemies can deplete your temp hp as this does not end the incapacitated effect.

You fight a CR 23 Kraken in it's lair ? Well... if you manage to hit AC 18 it doesn't matter that it has 5 legendary resistances. On it's next turn it cannot use it's 2 attack + Fling, Lightning Strike, or Swallow and it also cannot use it's 4 legendary actions or make an opportunity attack. In my opinion that is a tad bit too powerful for a level 3 spell, even if you have to cast it again every turn if or when the krakens minions take out your temp hp.

Quote from Runenstahl >>

My point is, that there is no other spell or effect that takes a target out of the fight that does NOT allow a saving throw (and therefore a legendary save for a boss). That is what makes this spell too powerful in my opinion.

You can use your turn to cast this 3rd level spell and make an attack. If it hits (and there are many ways to get advantage and other bonusses to help you with that) the target creature looses a turn. It really doesn't matter that the enemies can deplete your temp hp as this does not end the incapacitated effect.

You fight a CR 23 Kraken in it's lair ? Well... if you manage to hit AC 18 it doesn't matter that it has 5 legendary resistances. On it's next turn it cannot use it's 2 attack + Fling, Lightning Strike, or Swallow and it also cannot use it's 4 legendary actions or make an opportunity attack. In my opinion that is a tad bit too powerful for a level 3 spell, even if you have to cast it again every turn if or when the krakens minions take out your temp hp.

Totally agree. A single 3rd level spell forever (1 hour) taking out a CR20+ bbeg of combat screams "we didn't plan this spell out accordingly but we were given a deadline to add X amount of spells to the new book so we regurgitated an idea an intern had without proper QA" 

How many 3rd level spells is your 5th level wizard able to cast in one combat that they are able to cast SV 2 times and counterspell giving me my fireball back to cast again?

Quote from Isaragnor >>

how to beat selunes viper, have 2 enemies instead of 1. both can cast an aoe spell lets say fireball, average damage 28, your wizard or druid passes the save but are now basicly out of temp hp anyway, or you roll slightly better than average and the temp hp is gone even with a passed save. The player got to use their ability and feel good about it but it didnt break anything since you choose to have more than 1 person in the fight. 
the other solution is to have more encounters per day. every spell is amazing if im only needing to fight 1 encounter per day and always have all my spellslots

Why not Dispel Magic? No check to end Sylune's Viper. Recasting it is now vulnerable to Counterspell.

Also, I hope the caster wasn't needing that climb speed to stay in position ...

Quote from Isaragnor >>

How many 3rd level spells is your 5th level wizard able to cast in one combat that they are able to cast SV 2 times and counterspell giving me my fireball back to cast again?

Very easily! Sorcerer, Wizard, and Warlock get access to Counterspell. So if we had at least 2 of these 3 popular class choices, we can Counterspell repeatedly while the martials dunk of the incapacitated guy who is hit from SV.

If I'm a Warlock who at lvl 5 at least has a +1 Rod of the Pactkeeper, I can use a magic action to regain a spell slot. Meaning, I have Counter spell ready again! 

And if I'm a Sorcerer, I can take a Bonus Action to convert 5 sorcery points for another 3rd level slot. Another counterspell! 

And even with all that, with the Wizard/Druid having two 3rd level spells, this means we almost guarantee the BBEG lost 2 entire turns with no ability to use Legendary Actions/Reactions. It goes to more than 2 turns lost when we factor in the Sorcerer/Warlock counterspelling those fireballs meaning SV stays up. 

Sounds like you should just give your monsters the spell as well then. 

Quote from Isaragnor >>

Sounds like you should just give your monsters the spell as well then. 

Monsters with counterspell? Easy! I cast SV at 70 feet away (outside Counterspell range). Then, I walk up 20 feet and attack with SV safely.  

I was saying give your monsters SV.

Quote from Isaragnor >>

I was saying give your monsters SV.

Ah ok. In general, I don't like to use Stun/Paralyze/Incapacitate on players. I like to challenge my players with scenarios that they get a chance to react against, not steal their ability to play. 

As in, I like occasionally using monsters that deal more than 1/2 of the player's HP on round 1. But players can still react to that challenge instead of their turn being totally skipped. 

Its why I think SV sucks. Without a save, this just means the target gets completely shut off. There are infinite amount of ways to challenge players that don't result in removing their ability to play the game. I do think players have a better chance of getting around SV of course but, as I said, making them unable to play is not very fun for anyone at the table.

one more solution use some of the 25% of all monsters that are immune to the poison condition which then makes them ignore the incapacitated condition rider have said creature attack the caster. and use it in conjunction with other creatures ideally at minimum as many as there are players instead of one creature on their own. Then after that fight have another encounter or 2 in the same day where they have already now used their spellslots and cant use SV again since as you said they cast sv 2 times and counterspell once effectvely being out of 3rd level spells and now have to fight again without it.
Since the game assumes 4 combats an adventuring day use that so that your players dont have infinite resources for each fight.