Pong Krell, Betrayer

Flash

You may cast spells as though they had flash.

At the beginning of each upkeep, you may discard a card. If you do, the next spell you cast this turn has its converted mana cost reduced by the discarded
card's converted mana cost. When that spell resolves, Pong Krell, Betrayer deals damage equal
to the discarded card's converted mana cost to any target.