You draw a guillotine blade above your opponent. It falls on <him>, severing <his> head and dealing X damage. Let <him> eat cake!
or
You draw a sweet rainbow and a rad jet fighter, and then the jet fighter flies through the rainbow and the rainbow explodes and then the jet fires its machine guns and it's all rat-tat-tat-tat-tat and (10-20) (+10-20) (+10-20) (+10-20) (+10-20) damage.
or
You use the pencil to replace your opponent with a slightly shorter version of <itself>.
Monster attack power reduced by 30-39
Monster defense reduced by 30-40
or
You draw a crude doctor, who tends to your wounds the best that he can, given that you didn't remember to draw him a little black bag.