Nunu and Willump, Snowbound

When Nunu and Willump, Snowbound enter the battlefield, create a Snowball token. (It's an artifact with: "At the beginning of each player's upkeep, put a snow counter on it."
Whenever Nunu and Willump attacks, you may sacrifice a Snowball token. If you do, tap up to X target creatures, and Nunu and Willump get
+X/+X and gain trample until end of turn, where X is the number of snowball counters that was on th