I'm in the process of building this. It's a competitive, fun, and flavorful deck that builds up card advantage as Toothy quickly grows large enough to one-shot people. It has Jace, Wielder of Mysteries as another wincon.
A typical game:
Turn 1: land, mana dork
Turn 2: land, Pir
Turn 3: Toothy
Turn 4: card draw shenanigans and smashing face with Toothy
Turn 5-6: more card draw shenanigans, more face-smashing, and possibly casting Jace and bouncing Toothy for the win.
There's a few cards you can use to exile and return Toothy, which makes removal fizzle, gains you card advantage, and Toothy comes back twice the size (assuming Pir is in play).
I put reality ripple in there because it protects toothy from boardwipes and he keeps his counters. Spike weaver can target itself, adding an additional counter when Pir's in play, so you can fog forever. Isochron scepter and dramatic reversal are in there. Astral Cornucopia plays well with Pir and anything that proliferates.
Decklist
Approximate Total Cost: