Astarion's Thirst

Exile target creature. Put X +1/+1 counters on a commander creature you control, where X is the power of the creature exiled this way.

Agent of the Iron Throne

Commander creatures you own have "Whenever an artifact or creature you control is put into a graveyard from the battlefield, each opponent loses 1 life."

Biowaste Blob

Oozes you control get +1/+1.
At the beginning of your upkeep, if you control a commander, create a token that's a copy of Biowaste Blob.

Akroma's Will

Choose one. If you control a commander as you cast this spell, you may choose both instead.
• Creatures you control gain flying, vigilance, and double strike until end of turn.
• Creatures you control gain lifelink, indestructible, and protection from each color until end of turn.

Anara, Wolvid Familiar

During your turn, commanders you control have indestructible. (Effects that say "destroy" don't destroy them. A creature with indestructible can't be destroyed by damage.)
Partner (You can have two commanders if both have partner.)

Angelic Field Marshal

Flying
Lieutenant — As long as you control your commander, Angelic Field Marshal gets +2/+2 and creatures you control have vigilance.

Bloodsworn Steward

Flying
Commander creatures you control get +2/+2 and have haste.

Archivist of Gondor

When your commander deals combat damage to a player, if there is no monarch, you become the monarch.
At the beginning of the monarch's end step, that player draws a card.

Bastion Protector

Commander creatures you control get +2/+2 and have indestructible.

Bane's Contingency

Counter target spell. If that spell targets a commander you control, instead counter that spell, scry 2, then draw a card.

Agent of the Shadow Thieves

Commander creatures you own have "Whenever this creature attacks a player, if no opponent has more life than that player, put a +1/+1 counter on this creature. It gains deathtouch and indestructible until end of turn."