Generally, costing UUU is a deal breaker for constructed and a warning sign of an unplayable card, but over the past year-and-a-half, maybe for the first time in the history of Magic, having a mana-intensive casting cost has actually been a positive instead of a negative
Abominable Treefolk Abominable Treefolk only sees play in decks that care about snow permanents, though it's really good there
You gain control of Kain until end of turn
Bills, or more Magic cards
March can win the game on the spot when it draws six or more cards and slams your Craterhoof Behemoth
Your opponent may have the means to block your attacker, but if their defending creature is valuable and they think you have the means to take it out, bluffing a combat trick or interaction can give you a couple of free hits