Pain Magnification

Enchantment

Whenever an opponent is dealt 3 or more damage by a single source, that player discards a card.

The Rakdos make sure their victims remember their pain—or at least give up a little bit of their sanity in order to forget.

2006-05-01 If a source deals 3 or more damage to multiple opponents at the same time, this ability will trigger once for each of those opponents. They will each have to discard a card.
2006-05-01 This triggers only if all 3 or more damage is dealt at the same time. It doesn't trigger if damage that adds up to 3 or more is dealt at different times by the same source.

Card is in preconstructed decks:

mtg.wtf