Use antimatter! Antimatter! Antimatter is the weakness of everything build of matter including the atmosphere! ... DON'T use antimatter!!!
When ever possible in pen'n'paper rolegames I try to make use of wind spirits or air elements for the same reason @Saronite stated.
So everyone is gay for and in awe of MC? Isn't this the boy, who fucks up all the time? Contracting a magical beast, that could wipe out countries, feeding some spirits at home without telling anyone, burnig down the house of his friend's parents.... I'm also in awe.
Is it just me or are those eyes misplaced and creepy as hell?
Depending on how skilled someone is, most beings can be killed either with air or water magic. Air, by cutting off their oxygen supply and water by putting water in their lungs, drowning them in both cases.
Bit brutal, but hey, it works against most beings, and humans have so many weak points they don't need to use it against them.