well, i saw this play. it was the end, no resources, one side had one building and one dark templar left, the other side has a base, 3 dark templar, and no resources. the first player uses his dark templar to block the only ramp that leads to his building. when the three dark templar go to destroy it, they are blocked. the game is about to be called a draw when the second player merges two of his dark templar, allowing the last one to SLIDE THROUGH the entire blockage, and proceeds to destroy the pylon.