While Magicka certainly allows you to commit villainous acts against your co-op chums, you should probably be trying to work together. If the call of evil is getting too much for you and you're just pissing all your mates off, then there's some DLC on the way which should allow to scratch your bad guy itch. The Other Side of the Coin lets you play as the foul vampire Alucart (son of Tracula?) and his nefarious necromancer henchmen as they try to ruin everyone's day and attempt to kill Vlad, who is most certainly not a vampire.
There's a new story to play through, new challenge maps and the necromancer has been added to PvP where there will be even more opportunities for villainy, no doubt. It's planned for digital release on June 14 and will only set you back $4.99.