D&D 5E Question on using dispel magic against a summoned and planar bound demon.

[ECMO3]

The situation is a CR9 Demon was summoned with Summon Greater Demon using an 8th level casting and then bound for 30 days using Planar Binding cast at 7th level.

If someone casts dispel magic at 3rd level I have a few questions:

1. Does the dispel affect both spells and if it effects both do you make one spell casting check against an 8th level spell or two checks, one against 7th and one against 8th to see if it succeeds?

2. If you succeed in dispeling only one of the effects what happens to the demon?

 

[Tonguez]

I’d rule that the Summons magic already ended (when the caster was no longer concentrating) and only the Planar Binding is in place (including the effect that extends the Summons to 30 days).
So Dispell is cast v level 7 Planar Binding Only

now here’s the trick, if you do succeed in dispelling the binding, the demon stays around for an additional 1d6 rounds (as per Summon) and must be Banished instead

 

[M_Natas]

The problem is - Summon Greater Demon is not Teleport or Plane Shift or Something. The Caster actually uses his concentration to keep the spell running, to keep the demon here.
Planar binding says that it extents the duration of the summoning spell to 30 days.

So we have two ongoing effects here, the planar binding and the summoning spell. So when you read dispel magic it says you need to make a check for each spell that is affecting the target.
In this case: two.

But, if either spell is broken by dispel magic, the demon's goes back to the abyss either way.
Because if planar binding is broken, the time extension of the summon is gone and the time-limit for the demon ends and he goes back from where he came from.
If the summon greater demon spell is broken, the thing that keeps the demon here is gone, too.
If you want to keep for 1d6 rounds is up to you. There could be made a case for and against it.

 

[Paul Farquhar]

Rule of Cool applies: the demon is free to do whatever the hell it wants.

 

[aco175]

I like the rule of cool in this but likely give the player this one and let his send the demon back. I might be tempted to place an additional restriction on the roll like disadvantage for some made up reason such as they are in an evil temple to the demon god, but would allow something.

 

[kigmatzomat]

The way we handle this is assuming Dispel Magic sets remaining duration to zero. A spell with no remaining duration (fireball, planeshift) is unaffected.

Some spells, like True Polymorph and Wall of Stone become permanent after a duration. Catch it before then and it ends immediately.

Unless a spell notes "Permanent until Dispelled", i.e. True Polymorph, spells without duration cannot be dispelled.

This is a pretty simple test. Is there some clock ticking down after which the demon snaps back to the underworld (Summon & Planar binding), or is it effectively here forever because the magic opened a door (Planeshift/Gate) without the tag "Permanent until Dispelled"?

 

[Baron Opal II]

How we do it is that dispel magic can break the summoning, but once it is bound to the plane a banishment is required to send it back.

 

[UngainlyTitan]

The situation is a CR9 Demon was summoned with Summon Greater Demon using an 8th level casting and then bound for 30 days using Planar Binding cast at 7th level.

If someone casts dispel magic at 3rd level I have a few questions:

1. Does the dispel affect both spells and if it effects both do you make one spell casting check against an 8th level spell or two checks, one against 7th and one against 8th to see if it succeeds?

Not as far as I can tell, dispel only affects one spell.

2. If you succeed in dispeling only one of the effects what happens to the demon?

Nothing really.
If the summoner is not present I would say that the Planar Ally bound creature is the same as an uncontrolled demon if the summon spell concentration has been dropped. (it hangs around for 1d6 rounds) but as long as the Planar Ally is in place it is bound by its last instructions.
This may mean that it ignore the party.
So dropping Planar Ally releases the demon from that mission. It is now an uncontrolled creature.
If the summoner is still present then both effects are up.
Breaking the summons (By dispel or a concentration check) causes the summoner to lose the ability to issue fresh instructions to the creature. it will attempt to carry out its last mission until the planar ally spell is dispelled.
Breaking the Planar Ally will have no special effect as long as the Summons is in effect.

 

[ECMO3]

Breaking the summons (By dispel or a concentration check) causes the summoner to lose the ability to issue fresh instructions to the creature. it will attempt to carry out its last mission until the planar ally spell is dispelled.

Once you cast planar binding concentration no longer applies. There is no concentration on planar binding and casting that overides the duration on the summons, which is where the concentration comes from.

 

[UngainlyTitan]

Once you cast planar binding concentration no longer applies. There is no concentration on planar binding and casting that overides the duration on the summons, which is where the concentration comes from.

Well

PLANAR BINDING
With this spell, you attempt to bind a celestial, an elemental, a fey, or a fiend to your service. The creature must be within range for the entire casting of the spell. (Typically, the creature is first summoned into the center of an inverted magic circle in order to keep it trapped while this spell is cast.) At the completion of the casting, the target must make a Charisma saving throw. On a failed save, it is bound to serve you for the duration. If the creature was summoned or created by another spell, that spell's duration is extended to match the duration of this spell.
.....

I refer you to the bolded section of the Planar Binding Spell.