Eternal Witness

When Eternal Witness enters the battlefield, you may return target card from your graveyard to your hand.

Panharmonicon

If an artifact or creature entering the battlefield causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.

Authority of the Consuls

Creatures your opponents control enter the battlefield tapped.
Whenever a creature enters the battlefield under an opponent's control, you gain 1 life.

Teleportation Circle

At the beginning of your end step, exile up to one target artifact or creature you control, then return that card to the battlefield under its owner's control.

Abdel Adrian, Gorion's Ward

When Abdel Adrian, Gorion's Ward enters the battlefield, exile any number of other nonland permanents you control until Abdel Adrian leaves the battlefield. Create a 1/1 white Soldier creature token for each permanent exiled this way.
Choose a Background (You can have a Background as a second commander.)

Wall of Blossoms

Defender
When Wall of Blossoms enters the battlefield, draw a card.

Mistmeadow Witch

{2}{W}{U}: Exile target creature. Return that card to the battlefield under its owner's control at the beginning of the next end step.

Elvish Visionary

When Elvish Visionary enters the battlefield, draw a card.

Progenitor Mimic

You may have Progenitor Mimic enter the battlefield as a copy of any creature on the battlefield, except it has "At the beginning of your upkeep, if this creature isn't a token, create a token that's a copy of this creature."