Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
EDIT: Going ungeneric is my play. I don't think the Rock Blast part would have mattered though. -2 in Special Defense along with Toxic Spikes getting you, opened for Froslass to win 1-0 with Choice Scarf Shadow Ball.