Sol Ring

Inspiring Leader

Commander creatures you own have "Creature tokens you control get +2/+2."

Mountain

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.)

Plains

Arcane Signet

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