D&D 5E Homebrew Monster: Prismatic Hydra

[Sunseeker]

I'll probably run it as written, and add some HP if they are having too easy a time of it. I want it to be a challenge, but I don't want it to be a long boring fight. It should live long enough for each of the PC's to do at least one cool thing, and have some scary moments if they fail too many saves.

I do hope you get to spawn some of those more unique heads down the list. I think that'll really take your party for a spin.

 

[Caliban]

I do hope you get to spawn some of those more unique heads down the list. I think that'll really take your party for a spin.

I hope so too. I'm hoping it will be an epic fight for them.

 

[Olrox17]

5E CR guidelines are soft. I don't think extreme optimization needs to be assumed here at all, plus there's not much room for optimization from levels 6-11. There just isn't, and you don't even have access to the "big guns" of magic either.

A party of 5 fighters (who are neither complete morons nor total optimizers) could take this monster down in 5 rounds. They're going to dish out ~15 points per fighter, per turn, that's ~75 points per round, accounting for peaks thanks to Action Surge and crits and valleys from misses. At level 6 they will have a proficiency of +3, assuming they maxed their attack/damage stat that's +8 to hit minimum, so they only need to roll a 7 to hit.

The biggest danger here is the breath weapons, and the risk of melee-types simply not being in damage range. If your party is clever and the hydra is stupid, you can even get the heads to hit each other and 10d6 will, on average, nuke any other head.

So again, I'd give this monster about 5 rounds.

I believe you are underestimating the hydra's damage numbers (read Quickleaf's post for details). In any case, now we know that the OP's group is level 8, which should be enough to take down this thing (unless they spend too many resources before fighting it).

 

[Caliban]

I believe you are underestimating the hydra's damage numbers (read Quickleaf's post for details). In any case, now we know that the OP's group is level 8, which should be enough to take down this thing (unless they spend too many resources before fighting it).

Quickleaf seems to assume everyone is going to fail their saves against every single beam attack, every round. Not likely. I set the damage to be "all or nothing" - either you get hit by the beam or you don't.

Plus, the prismatic heads won't target the same creature (too chaotic) so the damage will be spread out (unless only one PC is available as a target).

Additionally - only three heads can use beam attacks on it's turn, the other two will bite. It needs to use legendary actions to get more beam attacks.

It should be a tough fight, and I may have overestimated how well my players will do, but I think it's within their capabilities.

 

[Caliban]

I ran the encounter tonight - it was in 100' x 100' room with several 10' x 10' platforms and catwalks around the edges and "pump controls" in the center of the room. The room was a central processing point and pumping station for trash and sewage in a massive sewer complex under the city. The hydra had taken up residence and city was unable to access the pump controls or the room itself, and trash sewage was piling up.

As they fought the hydra, if they dodged a beam attack it would take out a nearby portion of the platform or catwalk they were standing on, diminishing the available area to fight on.

The body of the hydra was under 10' of water, and the water was 10' below the platforms. They could have made it too the pumping station controls to lower the water level and expose the hydra's body, but they didn't think of it.

For the first two rounds they were certain I was trying to TPK them, partially due to several poor rolls on their part. But the Elven wizard bladesinger cast Haste on himself (Advantage on Dex saves), the bard turned himself invisible (for this combat I ruled it would give him advantage on Dex saves vs the beams because he was harder to target), the Aasimar monk and Dragonborn rogue just relied on their naturally high Dex saves, and the Tiefling fighter/warlock just had to tough it out and save his "Dark One's Own Luck".

I tried several times, but failed to send anyone to the Digestion Dimension (the Rogue failed herDex save twice, but made the Wisdom save once, and the Bard used Dispel Magic to end the effect before she was send to the DD - and the Fighter Warlock expended Bardic Inspiration and Dark One's Own Luck to avoid it.)

They focused on killing heads and not allowing them to regrow naturally - they killed about 7 heads, but only one was able to regrow two new heads, the other heads I had to use Legendary Actions to replace. At one point they had it down to a single head, then it regrew two and used Legendary actions to regrow another.

The finishing blow was dealt by the bard, with Vicious Mockery when it had 3 heads left. I described it as being so confused by the insult that the heads stared at each other in confusion, then one by one their heads exploded as it was unable to process it's conflicting emotions. Several PC's were bloodied, and the bladesinger was taken to zero HP just before they killed the hydra. (I did end up giving the hydra another 50 HP for the fight.)

Overall, I think it was a success.

 

[Stalker0]

I feel like the hydra is a bit too vulnerable to area effects. Heck a decent fireball could knock out all heads without fire resistance in one go.

 

[Caliban]

I feel like the hydra is a bit too vulnerable to area effects. Heck a decent fireball could knock out all heads without fire resistance in one go.

That's why I made the room so big. The heads each take up a 10x10 area and spread out, and move around every turn.

The wizard was able to get two of them in a fireball, once. They could have gotten three at one point, and another time four heads were lined up for a lightning bolt but they weren't able to capitalize on it.

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