The VOIDRUNNER'S CODEX is coming! Explore new worlds, fight oppressive empires, fend off fearsome aliens, and wield deadly psionics with this comprehensive boxed set expansion for 5E and A5E!
Another idea - since the LICH is immune to poison and disease..what about stocking the lich's lair with yellow mold and every other kind of toxic subtance which the players will be forced to step on, breathe etc....