Granted, the game is called "Waluigi's Statue", and involves Mario and Luigi trapped in a statue of Waluigi. There are many enemies that look like him, but Waluigi himself doesn't appear anywhere in the game.
Granted, but nothing changes (because it is already possible to do that (even have the picture have him), but he doesn't keep the mushroom for more than a few seconds.
Let's do this correctly. I wish enemies (all enemies that can receive one right now) in Super Mario Maker (and it 3DS remake) were able to receive 1 or 2 Super Mushrooms from the players and not lose them unless shaken.