Anyone who cracks lots of packs of Magic will have a mountain of unplayable Limited chaff. You know these cards. Here are two of them. All of the rules for this format are identical to Constructed, except all mana costs on the card are reduced by two colorless mana.
Here are two cards that cannot make it into this format because the mana abilities cannot be reduced by two colorless mana.
There cannot be any zero costs in this format either. Greater Sandwurm's Cycling cost would be zero in the Minus Two format: no way. This card cannot be in the Minus Two format.
Cards with any X costs also are not in the Minus Two format.
This is another no-go since in the Minus Two format, this would be a zero casting cost artifact and no zero casting costs of any type are allowed in the Minus Two format.
But for the cards in the format, things get interesting. Now your over-costed Limited chaff reads like Mythic Rares. Here Onward would be R, and Victory would be W. That's pretty cool, I think. Notice this X is allowed because it is the power of a creature, and does not change in the Minus Two format.
This one is a no-go because one of the halves does not qualify for this format.
And this card becomes awesome in the Minus Two format. Now, it's a WB 2/3 with a 2WU Embalm cost. That's considerably better than playing the card as printed.