Picking a boss

[Redhood101]

I'm guest DMing cause the normal DM will be unavailable this Sunday. I'm gonna run a little adventure about someone summoning devils to attack a town. I'm designing the final encounter, and I'm debating which devil to pick for the big final encounter.
There are four level 7 players. A fighter, rogue, monk, and a paladin (yes, he has turn fiend, and no, I have no clue what to do about it yet). For a final boss, I'm debating between a bone devil or an ice devil (both using their spear/polearm variants). The battle would take place inside of a large cavern or a grove. It would be the only enemy the players would face, so I feel like going with a higher CR would help keep it engaging. I don't want to kill anyone, but I also don't want the combat to become a bore.
I have seen the Matt Colville thing about action-oriented monsters, so I might go with something like that and type and homebrew one of them. Not sure. If anyone has any advice or any ideas, I'd love to hear them.

[Unoriginal]

I'm guest DMing cause the normal DM will be unavailable this Sunday. I'm gonna run a little adventure about someone summoning devils to attack a town. I'm designing the final encounter, and I'm debating which devil to pick for the big final encounter.
There are four level 7 players. A fighter, rogue, monk, and a paladin (yes, he has turn fiend, and no, I have no clue what to do about it yet). For a final boss, I'm debating between a bone devil or an ice devil (both using their spear/polearm variants). The battle would take place inside of a large cavern or a grove. It would be the only enemy the players would face, so I feel like going with a higher CR would help keep it engaging. I don't want to kill anyone, but I also don't want the combat to become a bore.


The Bone Devil is likely to be only a speedbump, against 4 lvl 7 characters, including one who does a *lot* of damage to Fiends and a Monk who can Stunning Strike them.

The Ice Devil would be an interesting boss, however.

That being said, it could be too tough if the PCs have to fight many encounters that day. If it's the only fight of the long rest or near it should be fine.

Something I suggest, to make the fight even more memorable: whoever summoned the Devils has summoned the Ice Devil inside themselves, in an effort to steal the Ice Devil's powers and authority over lesser Devils.

As a result, the boss's "first phase" has the summoner mostly in control, granting the boss the summoner's mental stats and the Ice Devil's physical ones as well as all the fiend's powers, but the boss is still of humanoid type. Personally, I would make them look like the summoner's skin stretched all over an Ice Devil's body.

Whenever the PCs inflict X amount of damage to the boss, the summoner has to make an opposed CHA check against the Ice Devil. If the summoner fails, they can't control the devil anymore and the Ice Devil burst out of the still alive summoner's body, in a grotesque and gory fashion.

(The Ice Devil would still have all the HPs lost and the effects the PCs inflicted on the first phase).

After that, it could go in different ways. The Ice Devil could be genuinely grateful/feel indebted to the PCs, and as such offer to stop their devils from attacking the town, provided the PCs do not attack them or prevent them from taking the summoner's soul, and resume fighting when/if the PCs refuse. Or they could just thank the PCs from freeing them, then engage in glorious combat against worthwhile adversaries on their own volition, knowing that if they die they'll just pop back in Hell without issues. Or it could just be too angry at the humiliation to desire leaving anyone in a miles-wide radius alive.



I have seen the Matt Colville thing about action-oriented monsters, so I might go with something like that and type and homebrew one of them. Not sure. If anyone has any advice or any ideas, I'd love to hear them.

Ignoring Matt Colville is generally on top of my list of advice and suggestions. You can use Legendary Actions and Lair Actions if you want to give your boss more to do during the round.

[thoroughlyS]

An ice devil seems like it has a good chance for a TPK, just looking at the CR. Of the two options, I would go with a bone devil, and then give it some legendary actions. I am unfamiliar with the variant you're talking about but I assume it makes it so the monster acts outside its turn? That would also be a good option.