Big build up to final battle with the wizard villain. The PCs fight their way through dozens and dozens of minions, near to single digit hp. I have no idea how they are going to fight him.
The Cleric drinks a potion of invisibility and uses it to move witht he PCs healing them during battle, dragging the wounded back out of harms way, etc.
Finally the cleric leaves the PCs (in a large linen closet) to scout as he is the only one with any hp or spells and they need to find the villain- whom they have never seen.
The wizard hears the cleric (Half Plate and no ranks in Move Silent), he is trying though. The wizard casts See Invisibility and the Cleric casts Harm (this was 3e and I had informed the Players early on that there would be a save- they agreed there should be and so there is).
Missed save. Cleric kills wizard with his mace and moves on.
“What are you looking for?” I asked the Player.
He informs me that he’s looking for the villain. I shrugged and they rest out the night in the linen closet of the villain’s castle.
The next weekend the PCs sack the castle, they kill the last of the minions and are disappointed to find that the villain is no where to be found (he’s dead on the floor of a guest room in the castle- they looted his body already and got lots of cool stuff from him).
So they start hunting for him. Two weeks of them doing nothing but hunting this villain and I proclaim that- “Harm no longer functions in my campaign. Period.”
Lots of disappointed Players asking why- I answer them not at all.
I have not told them until this moment. Two years they have searched for him, off and on, through another half dozen levels. They know he is up to something, but he's just hiding to well- dam him!