It's a game limitation. I (or anyone else) could come up with some zany justification for why gateway can't take indy commanders with the casting mage, but in the end it's just a game limitation and it isn't going to change.
It's a game limitation. I (or anyone else) could come up with some zany justification for why gateway can't take indy commanders with the casting mage, but in the end it's just a game limitation and it isn't going to change.