User blog comment:Miskos3/Fairy Tail 537: The Power of Life, Review/@comment-26184007-20170526151859/@comment-21119641-20170526164238

Considering a weakened Igneel dealt damage to a holding-back Acnologia, I can't say he is undefeatable.

Hell, it's possible Larcade's RIP could work on him (since it doesn't have a physical form like Pleasure does, it may have not been devoured). Buuuut, I don't think anyone else in the manga could stand up to him, his abilities were top notch and I can say I'm glad he didn't go down in a fight.