User blog comment:Miskos3/Episode 272: Fairy Tail Zerø: The One Who Teaches Magic, Review/@comment-190.58.249.5-20160221003339/@comment-7418318-20160221180728

It depends.

If a "villain" feels very strongly he's doing the right or necessary thing, it might give him power too.

Most FT villains don't really fall into that category, since they are usually either selfish pricks or totally batshit crazy.

But there is at least one exception: Erza Knightwalker. She surely didn't fight so hard because she liked the king so much, but she felt very strongly about her loyalty and duty and managed to come out equal to Erza Scarlet as a result... sure it's no perfect example since she wasn't a wizard, but it should get the idea across.

The same could apply to Acnologia. He seems to feel very strongly that the Dragons and Dragon Slayers need to be eradicated and maybe that is (either in part of fully) the reason why he's so strong, because he too uses the power of feelings, but in an entirely non-friend/non-nakama way.

Despite being filler, this could also apply to the KotSS arc, where Byro was OP as fuck, but once his confidence has been underminded, he suddnly loses to Gildarts quite easily. Maybe because he lost the boost that the power of feelings (from duty, loyalty and the conviction of doing the right thing for "the cause") gave him previously.

I really hope that in the future there will be antagonists who use the power of feelings too in such a fashion, to level the playing field and force the MCs to really work and think for the victory.