Polukranos, World Eater

Monstrosity was the keyword built to give big green creatures a mana sink, and this Hydra is the one that turned the mechanic into a removal engine rather than just a growth spurt. The split here is the whole point: pay double X plus a green to grow, and the same trigger fires X damage spread across as many of your opponents' creatures as you like. That makes it a one-card board wipe scaled to your mana, an answer attached to a 5/5 body that was already worth casting on curve. The restraint built into it is the reciprocal clause: every creature it damages deals its power back, so a careless activation can feed the Hydra to a board of midsize bodies and bury it. You are not pointing a hose at the table; you are choosing targets that die before they swing, and accepting the math when they do not. That tension (kill the right things, survive the answer-back) is what separates a good Polukranos turn from a blowout against you. It rewards waiting for the mana to make X large enough that the damage is lethal rather than a trade, and punishes the impatient player who monstrouses into a wall of equal-power blockers. The damage being split among "any number" of targets rather than locked to one is what gives it reach a single removal spell never has: at high X it sweeps small boards clean while the body keeps attacking.