Our party of 3rd and 4th level intrepid adventurers are trekking through the bowels of a Dwarf Fortress-inspired dungeon, and are attacked by an unholy abomination of a shadow-infused undead forgotten beast that took the form of an enormous burrowing worm. In the first round, it knocks half the party below 50%, and we mostly focus on spreading out, debuffing its attack roll for next round.
The second round, it lunges and swallows my paladin whole. On the up side, since it's dead, it's not murdering him to death with stomach acid, but that's about all the silver lining involved.
Except that it's undead, and my paladin has a symbol of Turning, which lets my paladin use Turn Undead like a cleric. His turn comes up, and he fires off a Turn Undead. Inside the undead Forgotten Beast. The DM ruled that given the location, it doesn't even get a chance to save, and the monster basically explodes as it's shoved outward in every direction by 35 feet. Through an incredibly lucky reflexes roll, my paladin lands on his feet as the head of the monster crashes down next to him, pulping the party pets and nearly killing another PC, and casually brushes bits of the monster off himself.
In a show of undead resilience, the head and 15 feet of the body lived on to fight another round or two, but I basically turned a major boss fight into a curbstomp battle. (Which was a good thing, the fight the normal way would have killed us all, More than half the party was unconscious or dying when it went down, after three rounds of combat.)