Lurrus + Morph

[Barook]

Can you cast Morph cards with Lurrus from the GY for their morph cost, e.g. Den Protector or Fathom Seer?

Edit: Apparently it works, as seen on MTGO.

[PirateKing]

Can you cast Morph cards with Lurrus from the GY for their morph cost, e.g. Den Protector or Fathom Seer?

Edit: Apparently it works, as seen on MTGO.

202.3a: The converted mana cost of an object with no mana cost is 0.

702.36c To cast a card using its morph ability, turn it face down. It becomes a 2/2 face-down creature card with no text, no name, no subtypes, and no mana cost. Any effects or prohibitions that would apply to casting a card with these characteristics (and not the face-up card’s characteristics) are applied to casting this card. These values are the copiable values of that object’s characteristics. (See rule 613, “Interaction of Continuous Effects,” and rule 706, “Copying Objects.”) Put it onto the stack (as a face-down spell with the same characteristics), and pay {3} rather than pay its mana cost. This follows the rules for paying alternative costs. You can use a morph ability to cast a card from any zone from which you could normally play it. When the spell resolves, it enters the battlefield with the same characteristics the spell had. The morph effect applies to the face-down object wherever it is, and it ends when the permanent is turned face up.

I bolded the relevant parts. Morph creatures have a CMC of 0, and you can cast them from anywhere you;re allowed to, so since Lurrus open the graveyard to play, and 0 is less than 2, game sees no reason to stop you.

[Fox]

Can you cast Morph cards with Lurrus from the GY for their morph cost, e.g. Den Protector or Fathom Seer?

Edit: Apparently it works, as seen on MTGO.

The cmc of a morph on the stack is 0, so this makes perfect sense. The more interesting question is whether or not you can have Lurrus + Illusionary Mask in play and...say Uro in the GY (note that Lurrus is just in the 60 for this to be possible). Can you take a 3 drop in the yard and cast it as a 0cmc spell through Mask? My guess is this works just fine.

Just checked oracle, they butchered the card as printed and added a superfluous condition that the card must be in hand (while being able to summon was perfectly harmonious with how magic works). So this becomes a hypothetical.

[the Thin White Duke]

The cmc of a morph on the stack is 0, so this makes perfect sense. The more interesting question is whether or not you can have Lurrus + Illusionary Mask in play and...say Uro in the GY (note that Lurrus is just in the 60 for this to be possible). Can you take a 3 drop in the yard and cast it as a 0cmc spell through Mask? My guess is this works just fine.

If I remember how Mask works, you still need to pay the CC of the creature, plus any additional mana, and announce how much you are paying to the mask. However, the new wording makes it more confusing (in my opinion).
In your example, you need to pay 3 for Uro but the "X" for the mask can be 0-3 and any additional mana you want to spend. Does that make sense?

[Fox]

If I remember how Mask works, you still need to pay the CC of the creature, plus any additional mana, and announce how much you are paying to the mask. However, the new wording makes it more confusing (in my opinion).
In your example, you need to pay 3 for Uro but the "X" for the mask can be 0-3 and any additional mana you want to spend. Does that make sense?

The cmc of any face-down spell is found in the upper right no matter how much mana you paid; the cmc on the stack is always 0.

[H]

Lurrus has some different wording than we might be used to and I think it actually has the answer to the question in that. It says you may cast a spell with a CMC of less than 2, not a card with CMC less than 2. So, I think the answer is yes, you can Morph anything out of the 'yard really, with Lurrus.

[FourDogsinaHorseSuit]

The cmc of a morph on the stack is 0, so this makes perfect sense. The more interesting question is whether or not you can have Lurrus + Illusionary Mask in play and...say Uro in the GY (note that Lurrus is just in the 60 for this to be possible). Can you take a 3 drop in the yard and cast it as a 0cmc spell through Mask? My guess is this works just fine.

Just checked oracle, they butchered the card as printed and added a superfluous condition that the card must be in hand (while being able to summon was perfectly harmonious with how magic works). So this becomes a hypothetical.

This hypothetical actually touches on why "summon" was not perfectly harmonious with how magic works [today]. Uro has an Escape ability which allows you to cast it from the graveyard, now under today's rules "summon" is just "casting a creature spell" but in the hypothetical world where summon never went away it's very possible that "escaping" doesn't count as "summoning" because the today rule for "summoning" may have meant from hand and not from anywhere.
Which means that maybe mas would work for Uro because Uro had an escape ability so maybe it counts as a creature you could summon, but if it was a different CMC > 2 creature the answer would be a clear no because you wouldn't have the ability to summon it.
Also, is morphing summoning? Because by the time morph was an ability "summon" had been replaced by "play."

[Fox]

Assume a Painter was in play on green, a morph would still trigger Glimpse. So too could these summon spells be countered by Remove Soul. It is an alternate cast (which is why you’d need Lurrus to work around the escape alternate cost, had they let Mask work as printed). If it were “play” that would not use the stack (between resolution of activated ability and creature being in play).

Summon has always meant you can point to a spell on the stack [or ‘batch’] and say “that’s a summon spell on the stack.”

[FourDogsinaHorseSuit]

Assume a Painter was in play on green, a morph would still trigger Glimpse. So too could these summon spells be countered by Remove Soul. It is an alternate cast (which is why you’d need Lurrus to work around the escape alternate cost, had they let Mask work as printed). If it were “play” that would not use the stack (between resolution of activated ability and creature being in play).

Summon has always meant you can point to a spell on the stack [or ‘batch’] and say “that’s a summon spell on the stack.”

Play absolutely uses the stack. From the compreshensive rules

Play
1. To play a land is to put a land onto the battlefield as a special action. See rule 116, “Special Actions,” and rule 305, “Lands.”
2. To play a card is to play that card as a land or cast that card as a spell, whichever is appropriate. See rule 601, “Casting Spells.”
3. (Obsolete) Casting a spell used to be known as playing a spell. Cards with that text have received errata in the Oracle card reference. See Cast.
4. (Obsolete) Activating an activated ability used to be known as playing an activated ability. Cards with that text have received errata in the Oracle card reference. See Activate.
5. (Obsolete) The battlefield used to be known as the in-play zone. Cards that were printed with text that contains the phrases “in play,” “from play,” “into play,” or the like are referring to the battlefield and have received errata in the Oracle card reference. See Battlefield.

The can be countered by remove soul and trigger glimpse only because the word "Summon" got replaced by "creature". As printed, a summon is not a creature. That is why the glossary includes this bit of eratta:

Summon (Obsolete)
Older creature cards were printed with “Summon [creature type]” on their type lines. All such cards have received errata in the Oracle card reference to say “Creature — [creature type].” (Many of these cards’ creature types have also been updated.) See Creature.

So we're having to make assumptions about what "summon" would mean today. Because even what you're saying about what summon had always meant is incorrect: Summon also was the card type in addition to being the verb used to put the card on the stack.

[Fox]

The beauty about the old cards is that they are quite reliable when it comes to meaning exactly what they say. When you look at Karakas and you see the word “Legend” in the activated ability, it’s literally telling you to look for “Legend” (which was only on creatures as Summon Legend). So when Mask says “You can summon a creature face-down...” it’s literally telling you to look for the word “Summon” which is found on every [not-artifact] creature, again as “Summon [x].”

As printed the card is unequivocally telling you that you would be allowed to specifically cast a spell (which is to say using the stack) through the Mask. It does not imply you that you are “playing” the card directly, without using the stack/batch (once Mask activation successfully resolves).

If we’re being really precise about “play” [today] that means we’re talking about a special action that doesn’t use the stack. Sometimes we have to use “play” and “cast” interchangeably [imprecise wording], but they’re not the same thing - only one of them requires a stop on the stack/batch.

There is some weirdness in the old cards where you might see wording like “...may not play...” when they mean cast, and the artifact creatures secretly having summon prefixes (because Summon and Creature are equivalent), RFG which became exile, etc... The thing about them though is that if you did what they said [meaning real cards, not dexterity cards], you correctly navigated the card.

I don’t understand why you’re implying that back in the old days we assumed things when we were casting creatures. They were summon spells, which means they were creature spells, which means they were creature cards. Illusionary Mask specifically tells you the only thing that face-down card you’re casting can be is a Summon card type, being cast as a Summon spell. Mask means exactly what it says: Summon as the noun and verb.

The one and only assumption you ever had to make about Illusionary Mask only came up when they began printing -X/-X effects (the power/toughness of a face-down creature).
—
To escape explicitly means to cast to the stack, as the reminder text says “cast”. So you escape it, it’s on the stack so now we look at the middle of the card to see the spell type - thus we can point to it and say it’s a creature spell on the stack, which is the same thing as being a summon spell on the stack.

This really doesn’t matter though because escape is an alternate cost and Mask is too - so they can’t work together...which is why you’d need a maindeck Lurrus to let you replace normal casting casting cost from the yard, through the clever workaround of Mask presenting Uro as a creature spell with cmc of 2 or less [for Lurrus].

^Now Lurrus is banned, but this should actually be a thing that works (Lurrus and Mask in play, Uro in GY being cast face-down). The errata hack-job they did on Illusionary Mask completely fabricates this requirement that the creature card in question be “in your hand.” This should be removed immediately; Illusionary Mask as printed explicitly allows any legal casting of Summon [creature] cards as Summon [creature] spells to the stack through its alternate face-down pathway. Illusionary Mask isn’t supposed to care what zone the Summon [creature] spell is coming out of, it only requires legal casting as a Summon [creature] spell to the stack.