Robby knows the implication of it won't go well in a don't mention me note, and he'll take it without question. However, at Midoriya's point about the mushroom, he does quirk a brow and pull a half-puzzled, amused smile.

"Yeah, I wasn't thinking about offering out floating mushrooms for people to hold onto them." Really, now. As funny as that is to hear. "But drying them or turning them into a liquid, using magic to bring out what they can do and use it on a beast? It's not nothing. I'm gonna see what I can do with them too--I know someone who can use ink to make stones pop off. Anyone can use them, too."

Which was a plus for all this. It wouldn't be worth bringing up if it was just going to be a him thing.