Vengern, the Inevitable

Suspend commander 1—{r}{r} (You may suspend
this card from the command zone. Commander tax
still applies to suspend costs.)
Flying, haste, double strike
Whenever Vengern, the Inevitable attacks, you
may discard a card. It gets +X/+X until end of
turn, where X is equal to the discarded card's converted mana cost. If this card was suspended, sacrifice it at the end of combat.