How is it that I can spend 5 white mana to cast Archangel Avacyn then her transformers cog, or her ability, triggers and she becomes a "red" Avacyn, the Purifier. What changes her color and why can't I put her in my Avacyn, Angel of Hope deck.
Why can't I put Elbrus, the Binding Blade into my M.I.A. deck(Magda, Imagecrafter, and Aphetto). How come it goes from colorless to black.
You might say "well the rules say that the border determines its color." I'll believe the "the cmc is equal to the amount paid for the front" but not the border. Why not "1{b}: transform Elbrus, the Binding Blade into Withenger Unbound" or make Avacyn cost a red. Wouldn't that be better than the side choosing the color it makes no sense. Although I think EB would be a bit more expensive to transform like maybe 7 or 13, IDK.
I tried to get Elbrus/ Withenger to work but they wouldn't load so quick summary:
Elbru is an artifact that cost 7 to play and 1 to attach it. Whenever the creature it's attached to transform it.
Withenger Unbound is a 13/13 creature with "Whenever an opponent looses the game Withenger Unbound get 13 +1/+1 counters"
So for 8 mana and a flyer, you get a flying, 13/13 trampling, imitating demon that gets bigger when a player dies.
Assuming you're playing the Commander variant: The reason is color identity.
Color identity is different from color; in general, this is the card's color plus the colors of mana symbols in the card's mana cost and rules text (C.R. 903.4). But the color identity rules consider both faces of a double-faced card, not just the front face, when determining its color identity (C.R. 903.4d).
And in general, you can't include a card in a Commander deck if its color identity has colors outside your commander's color identity (C.R. 903.5c).
Thus, for example, the card Archangel Avacyn has a color identity of red and white — not just white — because it has a red color indicator on its back face and white mana symbols in the mana cost on that card's front face (C.R. 903.4, 903.4d). This is so even though the card's front face neither is red nor has red mana symbols in its text. As a result, you can't include this card in a Commander deck unless your commander's color identity includes not just white, but also red (which isn't the case for Avacyn, Angel of Hope).
As another example, the card Elbrus, the Binding Blade has a color identity of black because it has a black color indicator on its back face (C.R. 903.4, 903.4d). This is so even though the card's front face neither is black nor has black mana symbols in its text. As a result, you can't include this card in a Commander deck unless your commander's color identity includes black. (Note that the color identity of Magda, Brazen Outlaw is red, not black.)
Why can't I put Elbrus, the Binding Blade into my M.I.A. deck(Magda, Imagecrafter, and Aphetto). How come it goes from colorless to black.
You might say "well the rules say that the border determines its color." I'll believe the "the cmc is equal to the amount paid for the front" but not the border. Why not "1{b}: transform Elbrus, the Binding Blade into Withenger Unbound" or make Avacyn cost a red. Wouldn't that be better than the side choosing the color it makes no sense. Although I think EB would be a bit more expensive to transform like maybe 7 or 13, IDK.
Elbru is an artifact that cost 7 to play and 1 to attach it. Whenever the creature it's attached to transform it.
Withenger Unbound is a 13/13 creature with "Whenever an opponent looses the game Withenger Unbound get 13 +1/+1 counters"
So for 8 mana and a flyer, you get a flying, 13/13 trampling, imitating demon that gets bigger when a player dies.
Color identity is different from color; in general, this is the card's color plus the colors of mana symbols in the card's mana cost and rules text (C.R. 903.4). But the color identity rules consider both faces of a double-faced card, not just the front face, when determining its color identity (C.R. 903.4d).
And in general, you can't include a card in a Commander deck if its color identity has colors outside your commander's color identity (C.R. 903.5c).
Thus, for example, the card Archangel Avacyn has a color identity of red and white — not just white — because it has a red color indicator on its back face and white mana symbols in the mana cost on that card's front face (C.R. 903.4, 903.4d). This is so even though the card's front face neither is red nor has red mana symbols in its text. As a result, you can't include this card in a Commander deck unless your commander's color identity includes not just white, but also red (which isn't the case for Avacyn, Angel of Hope).
As another example, the card Elbrus, the Binding Blade has a color identity of black because it has a black color indicator on its back face (C.R. 903.4, 903.4d). This is so even though the card's front face neither is black nor has black mana symbols in its text. As a result, you can't include this card in a Commander deck unless your commander's color identity includes black. (Note that the color identity of Magda, Brazen Outlaw is red, not black.)
EDIT (Sep. 27): Minor edit.