Spellbound Dragon 
Creature — Dragon
Flying Whenever this creature attacks, draw a card, then discard a card. This creature gets +X/+0 until end of turn, where X is the discarded card's mana value.
Legality
standardNOT LEGALpioneerNOT LEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL