Splinter, the Mentor

Menace
Whenever Splinter or another nontoken creature you control leaves the battlefield, create a Mutagen token.
Partner—Character select (You can have two commanders if both have this ability.)

Haunted One

Commander creatures you own have "Whenever this creature becomes tapped, it and other creatures you control that share a creature type with it each get +2/+0 and gain undying until end of turn." (When a creature with undying dies, if it had no +1/+1 counters on it, return it to the battlefield under its owner's control with a +1/+1 counter on it.)

Deceit

When this creature enters, if {U}{U} was spent to cast it, return up to one other target nonland permanent to its owner's hand.
When this creature enters, if {B}{B} was spent to cast it, target opponent reveals their hand. You choose a nonland card from it. That player discards that card.
Evoke {U/B}{U/B}

Donatello, the Brains

If one or more tokens would be created under your control, those tokens plus a Mutagen token are created instead.
Partner—Character select (You can have two commanders if both have this ability.)

Mutagen

{1}, {T}, Sacrifice this token: Put a +1/+1 counter on target creature. Activate only as a sorcery.