Assist Trophies and Pokemon

[Kitsu]

Maybe he could sniff out an invisible item box (actually just make the instance when he "finds" it, so you can't find it without him), and one of the players has to destroy it. This also provides an interesting twist after the player has already found the unique trophy: whenever Poochy appears on that stage again, the players could scramble to "unearth" the treasure first, and the one that does so gets a special bonus of some sort.