Play Magicka free until Sunday at 1PM PST. This is the full version of the game.
Plus get Magicka for just $2.49 until Monday as well (75% off).
You can also get the complete collection which includes all the DLCs for just $6.24 (75% off).
All prices on Steam are in US dollars and exclude tax. All games are digital downloads and require a Steam account and the Steam client to play.