Most horrifying things that the DMs have done to you.

[Sir Chuckles]

Deck of Many Things.

Cursed.

With a lure that made any character that touched it want to keep drawing cards.

In my group, the words "Deck of" has a greater effect than Dominate Person cast by an epic level specialist Wizard.

Recently, one character died due to the Deck. So they decided that the best course of action to bring him back was to keep drawing. I genuinely did not want them to do that, but knew they wouldn't back off from it. I did a terrible, terrible, bad bad DM move that I feel guilty for (but not enough to tell my players and rescind the action) and slipped the card out of the deck when they weren't looking. It's not the first time I've Sleight of Hand'd the Deck, but it's the first time I've done it 100% against their favor.

They ended up drawing every other card at least once, except two. Note that this is the Pathfinder Harrow version, which uses the full deck plus Jokers.