Anvilanche (a wordplay on anvil and avalanche) is a minigame that plays like reversed Spleef; other than destroying blocks, you summon falling blocks. The objective is to squish your opponent(s) and be the last player standing!
In Spleef, later in the game you would have to parkour across gaps, but in Anvilanche you'll also be hiking, trying to stay on top and wreak havoc to those below.