Dragon Egg

Defender
When this creature dies, create a 2/2 red Dragon creature token with flying and "{R}: This token gets +1/+0 until end of turn."

Swashbuckler Extraordinaire

When this creature enters, create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")
Whenever you attack, you may sacrifice one or more Treasures. When you do, up to that many target creatures gain double strike until end of turn.

Mountain

Elesh Norn, Mother of Machines

Vigilance
If a permanent entering causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.
Permanents entering don't cause abilities of permanents your opponents control to trigger.

Dragon Tempest

Whenever a creature you control with flying enters, it gains haste until end of turn.
Whenever a Dragon you control enters, it deals X damage to any target, where X is the number of Dragons you control.

Generous Gift

Destroy target permanent. Its controller creates a 3/3 green Elephant creature token.

Patron of the Arts

When this creature enters or dies, create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

Nadaar, Selfless Paladin

Vigilance
Whenever Nadaar enters or attacks, venture into the dungeon. (Enter the first room or advance to the next room.)
Other creatures you control get +1/+1 as long as you've completed a dungeon.

Command Tower

{T}: Add one mana of any color in your commander's color identity.

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.

Imperial Recruiter

When this creature enters, search your library for a creature card with power 2 or less, reveal it, put it into your hand, then shuffle.

Vesperlark

Flying
When this creature leaves the battlefield, return target creature card with power 1 or less from your graveyard to the battlefield.
Evoke {1}{W} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

Wall of Omens

Defender
When this creature enters, draw a card.

Karlach, Fury of Avernus

Whenever you attack, if it's the first combat phase of the turn, untap all attacking creatures. They gain first strike until end of turn. After this phase, there is an additional combat phase.
Choose a Background (You can have a Background as a second commander.)

Springleaf Drum

{T}, Tap an untapped creature you control: Add one mana of any color.

Karmic Guide

Flying, protection from black
Echo {3}{W}{W} (At the beginning of your upkeep, if this came under your control since the beginning of your last upkeep, sacrifice it unless you pay its echo cost.)
When this creature enters, return target creature card from your graveyard to the battlefield.

Sun Titan

Vigilance
Whenever this creature enters or attacks, you may return target permanent card with mana value 3 or less from your graveyard to the battlefield.

Phyrexian Dragon Engine

Double strike
When this creature enters from your graveyard, you may discard your hand. If you do, draw three cards.
Unearth {3}{R}{R}
(Melds with Mishra, Claimed by Gix.)

Reveillark

Flying
When this creature leaves the battlefield, return up to two target creature cards with power 2 or less from your graveyard to the battlefield.
Evoke {5}{W} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

Stirring Bard

Defender
When this creature enters, you take the initiative.
Mantle of Inspiration — {T}: Target creature gains menace and haste until end of turn.

Plains

Far Traveler

Commander creatures you own have "At the beginning of your end step, exile up to one target tapped creature you control, then return it to the battlefield under its owner's control."