Sneak Attack

{R}: You may put a creature card from your hand onto the battlefield. That creature gains haste. Sacrifice the creature at the beginning of the next end step.

Mountain

Alora, Merry Thief

Whenever you attack, up to one target attacking creature can't be blocked this turn. Return that creature to its owner's hand at the beginning of the next end step.
Choose a Background (You can have a Background as a second commander.)

Island

Shifty Doppelganger

{3}{U}, Exile this creature: You may put a creature card from your hand onto the battlefield. If you do, that creature gains haste until end of turn. At the beginning of the next end step, sacrifice that creature. If you do, return this card to the battlefield.

Command Tower

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

Guild Artisan

Commander creatures you own have "Whenever this creature attacks a player, if no opponent has more life than that player, you create two Treasure tokens." (They're artifacts with "{T}, Sacrifice this token: Add one mana of any color.")