You pay the costs for the target artifact card if you cast it. You may pay alternative costs rather than the card's mana cost.

You may cast that card this turn even if Silas Renn leaves the battlefield.

Silas Renn doesn't change when you can cast the target artifact card. For example, if you target an artifact card without flash, you can cast it only during your main phase when the stack is empty.

An effect that instructs you to "cast" a card doesn't allow you to play lands.

Casting the card causes it to leave your graveyard and become a new object. You can't cast it multiple times.

If you don't cast the card, it remains in your graveyard.

If your Commander deck has two commanders, you can only include cards whose own color identities are also found in your commanders' combined color identities. If Akiri and Silas Renn are your commanders, your deck may contain cards with white, blue, black, and red in their color identity, but not green.

Both commanders start in the command zone, and the remaining 98 cards of your deck are shuffled to become your library.

To have two commanders, both must have the partner ability as the game begins. Losing the ability during the game doesn't cause either to cease to be your commander.

Once the game begins, your two commanders are tracked separately. If you cast one, you won't have to pay an additional the first time you cast the other. A player loses the game after having been dealt 21 damage from one of them, not from both of them combined. Command Beacon's effect puts one into your hand from the command zone, not both.

An effect that checks whether you control your commander is satisfied if you control one or both of your two commanders.