User blog comment:IamJakuhoRaikoben/Chapter 381: Where Demons Live, Review./@comment-1359322-20140418183022/@comment-24066070-20140418184342

Interesting point, he also transformed into a lizard at some point, perhaps that lizard was one of his TO's rather than "normal" Transformation magic.

However, I think they learned it from Makarov or that he simply helped them awaken their latent TO potential.