Lim-Dûl's Paladin

Trample At the beginning of your upkeep, you may discard a card. If you don't, sacrifice this creature and draw a card. Whenever this creature becomes blocked, it gets +6/+3 until end of turn. Whenever this creature attacks and isn't blocked, it assigns no combat damage this turn and defending player loses 4 life.

From Magic: The Gathering.

Open the interactive version on https://mythscribe.cloud/app/tcg/cards/cms6o9lf36atvpb1hz60w16xq.