On paper, it seems pretty balanced and self-restricting, for sure there won't be any oppressive card with this ability
It also has generic potential in other blue decks, as a reasonable draw piece that interacts nicely with self-bounce
Lulu, Stern Guardian also lets you stun something thats coming for you, and even lock it down harder with proliferate
Commander is a multiplayer format after all
This isn't to say a card like Jumbo Cactuar doesn't have high potential when paired correctly , especially given how easy it is to apply trample with a simple green spell, but its main benefit will likely be using up an enemy's removal
You may not think of go-wide Aggro when you think of the Sultai (black/green/blue) color combination, but spend some time with Mothman and he may just change your mind.