Your parenthesis are wrong. You've got "attack = ( ( ( user.str * 4 ) + ( skill.power * ( ( user.atk / 2 ) / 100 ) ) ". There are two extra paranthesis in front of user.str. The same is true of the rest of your lines in that section. When I've got syntax errors those are the first thing I check cause it's what I typically screw up.