Jeweled Lotus

{T}, Sacrifice Jeweled Lotus: Add three mana of any one color. Spend this mana only to cast your commander.

Sol Ring

Wizard from Beyond

Create a Character (Any nonlegendary creature can choose this as its Background. It becomes legendary and can be your commander.)
Commander creatures you own are Clerics, Rogues, Warriors, and Wizards in addition to their other types.
As long as you have a full party, if an ability of a creature you control triggers, that ability triggers an additional time.

Present Arms

Exchange your library with another deck you own from outside the game. Shuffle your library.

Decorated Knight

Whenever Decorated Knight attacks, draw a card from your original deck if it's outside the game.