Metastatic Evangel

Whenever another nontoken creature you control enters, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Guardian of the Forgotten

Vigilance
Whenever a modified creature you control dies, manifest the top card of your library. (Equipment, Auras you control, and counters are modifications. To manifest a card, put the top card of your library onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card.)

Sai of the Shinobi

Equipped creature gets +1/+1.
Whenever a creature you control enters, you may attach this Equipment to it.
Equip {2}

Lae'zel, Vlaakith's Champion

If you would put one or more counters on a creature or planeswalker you control or on yourself, put that many plus one of each of those kinds of counters on that permanent or player instead.
Choose a Background (You can have a Background as a second commander.)

Master Chef

Commander creatures you own have "This creature enters with an additional +1/+1 counter on it" and "Other creatures you control enter with an additional +1/+1 counter on them."