Always play this card

From the moment Manamorphose was spoiled, I found myself thinking, “When wouldn’t I want to play this card?” Getting two in my second sealed pool at last weekend’s prerelease only confirmed its value. It replaces its mana, replaces itself, and, as a bonus, can fix colors. It turns your sixty-card deck into a fifty-six-card deck. If you’re in enough red or green to play a second-turn card in either color, is Manamorphose just strictly an auto-include?
My first thought in the negative was “it sure would suck to get a Manamorphose countered.”
But not really. After all, if they just countered your Manamorphose, they’ve gained tempo — but that would have happened anyway. Had they countered an actual value card or yours instead, you would not only have lost tempo, but also a play. That’s actually worse then a counter being burned on the Manamorphose. Note that following this logic, I don’t expect good control players to ever counter the ‘phose when they can just wait and burn your spell instead. So counterspells, not a problem.
I could also see the “I have too much good stuff” argument, but really, this is the same argument that has people playing sixty-two card decks when the minimum is sixty. Your deck always, always has X worst cards, where X is the difference between your deck size and sixty. Given the option to go down to a fifty-six card deck, you really, really should.
That leaves mana curve. In some decks, particularly Boros or Sligh-style aggro decks, your mana curve is low enough that many of your plays happen on one mana, and a two-mana thinning device messes that up. I haven’t experimented with any designs in Lorwyn-Shadowmoor megablock or in Standard to see if that applies, but I can imagine it doing so.
In the meantime, the main question for all my block designs will be “does this deck provide enough red, green, or red and green to support using Manamorphose?” The basic qualification should be that its a second-turn playable almost all of the time. I suspect that most designs in block that support the right colors at all will support this play, making Manamorphose nearly a requirement.
Welcome to the world of fifty-six-card decks.