My Larvitar is poisoned with 10 HP left. My opponent has one prize remaining and no cards in the deck. Can I attack with "Mountain Eater" and win the game?
You can attack, but if you can't discard the card you don't get to remove two damage counters. Larvitar will be KO'd between turns and your opponent will take the last prize.
Source: Unleashed FAQ (2010-05-13), PUI Rules Team (2010-05-13)