Gargantuan Slime

At the beginning of your combat step, sacrifice a creature. Gargantuan Slime gets
+X/+Y where X is twice that creature's toughness and Y is twice its power. If tapped creature had first strike, Gargantuan Slime gains first strike. The same is true for vigilance, haste, lifelink, double strike, deathtouch, trample, hexproof and flying.