Talk:Fizz/@comment-26571276-20160331133126/@comment-24882239-20160412032222

Pen doesn't work the way you think it does. You can only penetrate what resistances they have, so you can't go below 0/  If you have 66 pen and they have 30 magic resist, you will simply do the full amount of magic damage to them, not extra (basically true damage that can be reduced by random things like Alistar ult).

Reduction works exactly like you think it does though. You can reduce magic resist below 0 (at least on other champions), at which point you will be doing more damage, but your pen will be completely useless at that point.

Also, quick note for how pen and reduction stacks:  flat reduction then % reduction, then % pen, then flat pen. Basically reduction is calculated in favor of the target while penetration is calculated in favor of the attacker.