Hideaway Manifest Cradle of the Accursed.

A really nice mechanic combo. This is like Write into Being, but generally better and as a colorless land. I would certainly think of putting this at rare. Maybe the activation cost could contain ?

I've bumped the card up to rare and am considering raising the manifestation cost from to . I don't want to add green to the card for both cube design reasons and the flavour reason that morph/manifest magic is supposed to derive from Ugin and feel colourless.

Onto the power level. Write into Being was designed for play in a limited format designed around Gray Ogres being somewhat playable. And the card functions as a Grey Ogre with an ETB pseudo-Scry 2 trigger with an off chance of manifesting.

A land that etbs tapped is a huge disadvantage and proportionally allows a larger upside. Contrast Myriad Landscape with Warped Landscape and Blighted Woodland. And that for Myriad Landscape the price of it entering the battlefield tapped allows it match the combined strength of the other two cards.

The theory with this land is that it entering the battlefield tapped lets you keep it after using it once, with it being to Cradle of the Accursed what Myriad Landscape is Warped Landscape. And since the average cost to make a 2/2 without spending card is around four mana (Nimble Innovator, Graff Harvest, Master Trinketeer), a colourless tapland should pay for a one-off ability to make a 2/2 without spending a card. However the question becomes does the capacity to manifest it justify bumping the activation cost up to five mana?

Okay two things that make most of your points moot in my eyes.

1) Manifested creatures aren't really Gray Ogres, since any one of them that are creatures can suddenly be turned face up to something (possibly huge) as a combat trick. If there are morph triggers around, it pronounces this even more. You seem to refer this offhandedly in your last sentence as if it wasn't the most important thing about manifesting.

2) I don't know about you, but I think Myriad Landscape is a mistake very similar to Wayfarer's Bauble. It is specifically only used and printed for Commander so it probably falls into that Chaos Warp territory. Personally, I take 'colorless breaks' that much more bitterly since adding a color to a card rather than removing one will always be the more interesting choice.