Dimir Archmage

Menace, skulk
Deathtrap (Whenever this creature blocks, you may discard an instant card. If you do, target creature blocked by Dimir Archmage gets -X/-X until end of turn, where X is the converted mana cost of that card.)
{2}{u}{b}: Return target instant card from your graveyard to your hand. Target player discards a card. Activate this ability only once each turn.