Probably a suicune. It looked like the pictures in Circinus' book.

[A little while ago, Armin got the little voltorb a children's book on legendary pokemon. Maybe not the most scientific source, but still, what he had seen had closely resembled just one pokemon in that book.]

I recorded it. I'll show it to you later.

[Right after they've completed this very important research.]

Ah, could you draw it? You are better at it than me.

[He could ask Polo but Polo only draws muscles, not paw prints.]