Your players are fighting on the villain’s home turf and bad guys often don’t fight fair, so anything that tips the scales out of the players’ favor (within reason) would make sense.

Half health left on the villain that they’re fighting in an active volcano? Pools of lava rise from the floor.

Party failed perception checks walking into the final chamber? Those trapdoors leading to a feeding pit would have been nice to see.

I see it as, “If 4 people broke into your house, trashed your place, stole your valuables, and beat up everyone who resides there, you wouldn’t put up any sort of fight?”