Mulligans
General Mulligans
The best cards to keep are Fire Fly, Black Cat and Tar Creeper as the generally good early game cards.
Aggro Mulligans
Fire Fly is a automatic keep. If the deck runs weapons, Ooze is a good keep. Tar Creeper is another obvious choice along with (arguably) Black Cat.
Control Mulligans
The General mulligan applies with the exeption that a slow card like Arcane Intellect would be a viable keep against certain slow control decks.
I am one of many that sees a new meta coming where Cubelock is the deck to beat. As we all know, Cubelock is a hard deck to beat, but its not impossible. One of the notable weaknesses we know of is that Cubelock struggles against agro/tempo decks when it doesn’t draw its early game defensive cards. This deck exploits that target Cubelock has on its back. I theorize a meta where many play agro so they can beat Cublock and its against those decks that this one will shine.