I've said it before and probably will do so again: I know Oda wants us to think Imu is the Super Ultra Mega Supreme Boss of all Bosses, but I'm still not impressed, because it's all because he just has the most ridiculously broken and overpowered Devil Fruit in the series.
Basically, he doesn't have to go with a consistent theme or power and is just basically a low-level reality warper who can do whatever he wants. If anything, I'm surprised he can't summon ghosts of people who had the Covenants like Saturn and Harald.
But again, I say, big fucking deal. If even a loser like Spandam had this bullshit, he'd probably be invincible, too.