Command Tower

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

Arcane Signet

Sol Ring

Sarulf, Realm Eater

Whenever a permanent an opponent controls is put into a graveyard from the battlefield, put a +1/+1 counter on Sarulf, Realm Eater.
At the beginning of your upkeep, if Sarulf has one or more +1/+1 counters on it, you may remove all of them. If you do, exile each other nonland permanent with mana value less than or equal to the number of counters removed this way.

Dosan the Falling Leaf

Players can cast spells only during their own turns.