I think The Skeleton Demolitionist is a fair bit overtuned, especially considering the tiny spaces you're usually forced to fight him in and how unavoidable most of his attacks are. His attacks seem to do 100-200 damage and are incredibly fast, while he's also incredibly fast and can be on you and blasting you for hundreds of damage in an instant. Again, all this while you're frequently forced to fight him in the tiniest of tiny spaces is simply too much.
Added on to that, I'm not a fan of the DPS check at the end where you have to kill him before he fires his weapon or you're most likely dead. I've practiced dodging it before, but again, tiny enclosed spaces make that very difficult, as does the ridiculous size of the instakill projectile. Dying to that doesn't feel fair or fun.
I had a deathless run going until I got to him. The only other time I even came remotely close to being in danger was against the Roc, another miniboss from your mod with a jacked up power level, who got stuck under a flying island and kept shooting me with a rapid barrage of projectiles that go through blocks, hit hard, and are difficult to avoid due their quantity and spread. I barely survived those cheesy attacks from the Roc, but the Demolitionist killed me twice.
I've fought these minibosses many times now. The fights range from not-too-bad to practically impossible to survive depending mainly on the luck of where they spawn and how their AI behaves (getting stuck behind blocks, trapped in rooms where you die if you try to enter, etc.). The Demolitionist is obviously the worst for that, since the dungeon has so many places for him to spawn where trying to get close to him is suicide (the attached screenshot with the instadeath room is from my fight today). If you can't find some way to control the spawns so that these issues don't happen, or at least aren't so common, I think the power level of the bosses should be brought down. The Demolitionist's damage needs a nerf regardless, though.
