See Vote 2 - Bottom up ideas.

I feel like the right way is that the comp rules say "when you turn an instant or sorcery face up, its owner puts it onto the stack, if they don't, they put it into their graveyard" so it all happens as part of the "turn face up" action, and isn't an ability that other game effects can mess with.

To me, that feels the right principle.

But I don't know if there's anything that still breaks it?

(It would also be possible to have enchantments with sacrifice effects instead of sorceries. I'm not sure if that's better or worse.)

Even if it can be made to work, there are just way too many in-depth rules issues that I don't want to deal with. I would rather just not do Spellmorph at all.

Putting things on the stack without casting them doesn't work, because it's during the action of casting that you select targets and modes and such.

Seems pretty clear that we can get it to work if we want it:
Just make:
Spellmorph x
Mean "Instead of casting ~ as normal, you may pay to cast ~ as a face down card, making it a 2/2 morph creature. Then, you have the ability to reveal ~, pay x to cast it"

(Arguments as to 'cast' and 'play' can be had; but 99% of the time won't matter, chose whichever makes it most like creature-morph)

Alternately; you could just avoid the issue and have normal morphs that have "When ~ is turned face up..." effects. If you really like, have a cycle of 0/0 creatures with that.

I've no strong preference either way.

I think it's a good idea -- I think it's obvious what's SUPPOSED to happen in essentially all cases, so I've faith the comprehensive rules can be fixed up, and I don't think that's a reason not to do it.

But I don't mind if we end up using morph in this set.

I wonder if something like this might work:

Spellmorph (You may cast this face down as a creature for . It can't be turned face up. You may cast it from the battlefield for its spellmorph cost.)

­Break Open probably still causes issues with this as it would with other versions of Spellmorph, though slightly different ones.

The main issue with Spellmorph and the Comprehensive Rules is that that having an Instant or Sorcery card on the battlefield at any time is an utter no-no. With all interpretations I've seen of the ability, cards like Humility and Sudden Spoiling combined with something like Break Open really screw it up, as do things like Stifle and Voidslime.

Link: I really don't think having an instant/sorcery on the battlefield for as long as it takes to check SBAs is a problem. Any more than having an unattached Aura on the battlefield is a problem, or having an Equipment attached to something that's no longer a creature, or indeed having duplicate Legends. That's precisely the kind of tidying up that SBAs are meant for, and I think they solve the corner case of Humility pretty completely.

­Stifle/Voidslime really shouldn't be an issue. Whatever ability is casting spellmorph has to only turn the card face-up at the moment it's about to be put on the stack. Either if you Stifle the spellmorph ability the creature doesn't get turned face up at all, or it's a "special action" like morph itself which can be done at faster-than-split-second speed, just like Willbender and friends.

So I think a variation on your wording would be fine:

> Spellmorph (You may cast this face down as a 2/2 creature for . You may cast it from the battlefield for its spellmorph cost. If it turns face up any other way, put it in your graveyard.)

That said, if you're really against the SBA to tidy up battlefield instants, then yes, I think your "It can't be turned face up" wording is okay. You'd have to indicate when you cast one whether the card being morphed was a morph or a spellmorph, which is a little bit of a pity.

But I don't think it's worth nerfing a mechanic for interactions with two old corner-case cards (Break Open and Ixidor, Reality Sculptor). If things go a little bit weird with those, but otherwise work fine, I don't think that's a big problem.

Well, when you copy a spell, you don't cast it either. But usually the effect allows you to choose targets. Modes we don't worry about for now as long as the cards we make are simple.

We need to consider two conditions: the base and the modifications by an ability. The base rule is when the spell is in play for no reason or has no ability that allows it to be cast (e.g. Break Open, Humility). In this case, it goes to the owner's graveyard as a state-based action. The modifications are instructions by various mechanics and abilities. In our case, what happens when we activate Morph to turn it face up. As part of the resolution, the controller may cast it as it is turned face-up. If not cast, then the SBA for the base rule kicks in and puts it in the graveyard.

So Spellmorph reminder should be something like this (changes to Alex's version):

Spellmorph (You may cast this face down as a 2/2 creature for . You may cast it from the battlefield face-down for its spellmorph cost. If this remains on the battlefield face-up, put it in the graveyard.)

How about "You may turn it face up and cast it by paying its spellmorph cost"?

this is closest to current morph reminder: "Turn it face up any time and cast it for its morph cost."

I think casting it directly as in my wording is probably safest. That way the spell side is never on the battlefield.

As long as it's on the battlefield face-down, it'll be on the battlefield even as you turn it face-up to reveal that you're casting it. So why even avoid it?

Just make a SBA for such an occasion it sticks around. Even if it's not because of morph (such as some weird spell that puts a card face down on the battlefield), the comprules need to be more explicit about it anyway. But obviously it hasn't happened yet. That's why there's so much confusion. People (rules makers) keep avoiding the issue, instead of making sensible rules to clarify what happens in such a case.

So we're just helping it along. Morph is one reason, but not the only reason the SBA should exist. It would allow other mechanics and spells to put spells in play and open up design space, without the need to argue about unexplained or unusual interactions.

In short, this SBA should already exist in the comprules, as it deals with all intended and unintended effects and side effects. Wizards don't make new mechanics and gives up just because it doesn't work with existing rules. They change the rules so the mechanics work as intended. Otherwise DFCs would never see the light of day. So that's what we're doing here. We can make face-up spells work with a simple SBA and a new keyword that gets around that SBA under specific conditions. Meanwhile a whole new huge area of design has been opened up with this simple SBA.