Here's a specific example: make an MDFC creatures as follows.

Side A: Legendary creature with a mono-green casting cost.

"Side A can only be your commander if each non-land card in your starting deck is Green [and monocolored]."

Side B: Sorcery with a UWRB casting cost.

"Side B can't be cast."

Might need it to be *be* all colors rather than say that it is, I suppose...

Can't you have the commander say:

(1) [This card] is all colors.
(2) [This card] can only be your commander if every non-land card in your deck is Green.

My vote would have to be for Nebraska here

Callan

radley

Ob nixilis!