Arcane Signet

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

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.)

Mountain

Lightning Helix

Lightning Helix deals 3 damage to any target and you gain 3 life.

Island

Ruhan of the Fomori

At the beginning of combat on your turn, choose an opponent at random. Ruhan attacks that player this combat if able.

Plains

Aurelia, Exemplar of Justice

Flying
Mentor (Whenever this creature attacks, put a +1/+1 counter on target attacking creature with lesser power.)
At the beginning of combat on your turn, choose up to one target creature you control. Until end of turn, that creature gets +2/+0, gains trample if it's red, and gains vigilance if it's white.

Chaos Warp

The owner of target permanent shuffles it into their library, then reveals the top card of their library. If it's a permanent card, they put it onto the battlefield.

Sol Ring

Abrade

Choose one —
• Abrade deals 3 damage to target creature.
• Destroy target artifact.