User blog comment:BlackWizardZeref/Fairy Tail Chapter 394: Juvia vs Keith Review/@comment-188.71.216.109-20140730125810/@comment-9595671-20140730164034

I see what you mean, it should be like Cana with Fairy Glitter as she only know how to cast it when Mavis gave her a free one use cast twice.

He's already learned how to manipulate it while he fought his father, so I think he already knows how to learn. In fact maybe the tattoo only gave him the experience on how to fully use it and after it goes away he still knows how to use Ice Devil Slayer magic but he lacks experience with it and can't use it well just yet.

Kinda like how when someone first starts riding a bike they need to learn how to avoid using training wheels, then they have to learn how to use tricks.