User blog comment:Real Godisme/Chapter 479/@comment-25111584-20160328140249/@comment-25111584-20160328165608

I'm talking about how Lucy evaluated power levels during the GMG. Surely she can do the same here?

Natsu's fiery aura is easily bright enough to render Jacob's Stealth useless, as well as enough to greatly reduce his all his stats, from agility to composure. I don't see the problem.