This card can do some crazy fun things, but it can also just do useful things, like powering down a creature with a bunch of counters, killing a planeswalker, or knocking back the energy player
Jalira, Master Polymorphist $1 Polymorph has seen competitive play from time to time, but this is much worse because you have to let it sit around for a turn before you can activate it
Just as Burn struggles to win with Lightning Bolt alone, you need a cheap creature that generates value over time in order to really maximize your mill count, and the Crab is simply best-in-class
Smee is basically the unsung hero of any Pirate crew
This card reminds me of Drannith Magistrate in some ways, but its certainly a much less oppressive version of that card
So, if you combine First Day of Class and one of those creatures with a sacrifice outlet, the Persist creature can just be sacrificed as many times in a turn as you want