I've also thought about "ETB phased out" as a possible land drawback: it's just like ETB tapped except it doesn't work with Amulet of Vigor or other untap shenanigans, it doesn't trigger landfall, and it doesn't allow your opponent to pick it off with Stone Rain or Tectonic Edge until you actually get a chance to use it for mana.

Here it essentially serves the purpose of a Wrath-proof shroud creature, even if not all that threatening.

But... If it's phased out, it doesn't exist. If something doesn't exist, can it enter the battlefield, let alone engage in combat?

Sure it can attack. I don't know so much about the 'dealing combat damage' part...

Nothing prevents phased-out creatures from dealing or receiving combat damage, except that the act of a creature phasing out is explicitly stated as removing it from combat. Here it never phases out, it just always existed that way, with the card text accounting for how it can enter combat in the first place from phaseland.

"ETB phased out" works by perfect analogy with "ETB tapped". They're both nothing more than the preemptive setting of one particular status. It won't set off the usual ETB triggers, but them's the breaks.

You know, I didn't give this much thought at first, but I kind of like the idea of a set focusing on phased out of play. Cards that hang out in limbo, do their own thing, and interact with each other in some sort of super-shadow world. It would make a pretty cool block.

Are there any precedents? I don't know how the original phasing rules worked, but the current rules say "Except for rules and effects that specifically mention phased-out permanents, a phased-out permanent is treated as though it does not exist. It can‘t affect or be affected by anything else in the game," which to me sounds like it would need an exception for dealing combat damage as well (and for untapping in the untap step? but not for having combat damage removed AEOT?).

Have I misinterpreted something? Does "attack and block" include dealing combat damage? I wouldn't have thought it normally does: it something says "can't attack" it normally still deals combat damage if its already attacking.

But assuming the wording works or is tweaked, yes, a very interesting idea that does just about work in the rules! :)