Can a demon summoned by the Summon Greater Demon spell be summoned into and contained by the spell's blood circle?

Question

Can a demon summoned by the Summon Greater Demon spell be summoned into and contained by the spell's blood circle?

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I'm designing a character who can summon demons and bind them with Planar Binding.

The Dybbuk, in particular, is one demon which I'm drawn to due to its ability to possess any Large or smaller humanoid or beast corpse regardless of CR and the only real drawback is the fact it's undead and loses any class features, although it would still be able to use things like innate spellcasting. Its at-will Dimension Door is also extremely useful and I can think of numerous applications.

I described the Dybbuk as the example of focus to highlight that the reason I'm choosing not to just summon it into the Magic Circle is due to the fact that it can teleport at-will. So, while it can't just walk out, I'm extremely doubtful it's going to fail 600 Charisma saving throws during the hour I would be taking to cast the Planar Binding spell. By using a Hallow spell that allows fiends inside the area but disallows teleportation and extra-dimensional travel, this can be stopped but just adds even more expense and a whole 24 hours (and hence, a level of exhaustion) necessary time for preparation.

So, my solution is cast Summon Greater Demon for the Dybbuk into a Glyph of Warding. Since I have to actually cast the spell I'm storing, and can draw the blood circle as part of the casting, I would draw it around the Glyph in which the spell is stored. I would then trigger it so the Demon can be present without my concentration while I concentrate on the casting of Planar Binding.

Hence, since the description of the spell's blood circle only states that the demon cannot cross it (or target anyone in it), does this work inversely as the actual Magic Circle spell can?

Please note that I am not exactly looking for alternatives to this method, but am completely open to them. However, I mainly wish for the question to be answered based on RAW and RAI reading, as well as what you all think would be reasonable.

Answer 1

Yes, if the demon is small enough to fit in the circle.

Two parts of the spell description for Summon Greater Demon (XGtE, p. 166) lead me to this conclusion:

The demon appears in an unoccupied space you can see within range

and

As part of casting the spell, you can form a circle on the ground with the blood used as a material component. The circle is large enough to encompass your space. While the spell lasts, the summoned demon can’t cross the circle or harm it, and it can’t target anyone within it. Using the material component in this manner consumes it when the spell ends.

The spell doesn't explicitly say you can't put the demon in the circle, only that the circle is large enough to encompass your space, and that you summon the demon in an unoccupied space you can see. There's nothing stopping you from drawing the circle, stepping away, and summoning the demon inside the circle.

Answer 2

Put Planar Binding into the Glyph of Warding instead

Your goal is to summon and bind a Dybbuk into service, and your problem is that you cannot contain it in a Magic Circle as commonly done, as the probablity that it will be able to make a Charisma save within one hour that you need to cast Planar Binding approaches certainty, and so it will be able to Dimension Door out.

Instead, you propose to summon it into the blood circle that normally would protect you to imprison it. The demon is medium sized, so it would be no problem to summon it into the circle. It however is unclear if the demon could not also Dimension Door out of the blood circle. The blood circle says:

the summoned demon can’t cross the circle or harm it, and it can’t target anyone within it

Dimension Door does not use the term target in its description:

You teleport yourself from your current location to any other spot within range.

The spell refers to the caster as "yourself" and the location to teleport to as a spot within range. It would be up to DM interpretation if the "yourself" counts as a target (and the fact that another creature can be taken along further softens this). So the demon might be able to cast Dimension Door. It also would be up to DM interpretation if teleporting out would count as "crossing" the circle or not. So you are at the DM's mercy here.

None of this is needed. You instead can pre-cast Planar Binding into the Glyph of Warding, triggering on the condition of the demon being summoned. Long casting time spells can be stored in the Glyph without problem. Since Planar Binding says

the target must make a Charisma saving throw

it is targeting a creature, and hence is elegible to be stored in Glyph of Warding.

You need to cast the Glyph at high enough level to store the application of Planar Binding you have in mind. If you for example were level 12 and would have two sixth level spell slots, you could cast both the Glyph and Binding on sixth level to secure 10 days of service.

Once you summon the demon, the glyph triggers, delivering the binding instantaneously. There is no need to contain the demon in the blood circle (or even summon it into the circle -- this approach also works with larger demons).