Demogorgon for a level 5th party?

[SorrySleeping]

Long story short, party's healer critical failed on magic (Spheres of power drawback he took) and created a zone of darkness centered 30ft away from the caster. They are in a small cave and just killed some giant insects, so lots of blood.

I wanted it to make a tough and special fight for them. I try to do something weird whenever a player with "Wild Magic" fumbles his magic.

What CR creature would be a good fight for a fifth level party of three?

[Scrapper]

Fire Breathing Dire Bunnies...
May have to combine a few templates, but 3-4 critters of around CR 4, but scattered about the cave so they only encounter 1 at first, but hear the others in the distance, think Aliens...

[Java Man]

Crawling puddles of venomous darkness (stats of a spider swarm, vulnerable to light in some fashion, any victim that succumbs to the distraction ability is also blinded for the same duration.)

[Brother Fen]

Gibbering mouther or two.

[Sunshine Rat!]

Just use the real Demogorgon. It would be hilarious with a fifth level party.

[Tinalles]

Hrm. Ideas for what you could do with a zone of darkness like that.

- It could be a stable gate to the Shadow Plane, allowing passage back and forth; you could have a couple of Gloomwings pop out. After cleaning up the Gloomwings, they have to figure out what to do about this gate they've created -- you could do a whole side-quest revolving around closing the gate or setting up guards to prevent strange shadow-things from passing through. Or they could go visit the Shadow Plane and see the Shae.

- It could be an unstable rift to the negative energy plane. Creatures cannot pass through it, but it's going to slowly spread until it engulfs the world (might take a few centuries though). It needs to be shut down, but the PCs will likely have no idea how to do it at level 5. Could lead to a whole campaign arc.

- The darkness is actually just a prelude; after a couple minutes, the darkness dissipates. At its center, the party discovers an unconscious woman curled into a protective ball around some kind of egg. When she wakens, she is confused, unsure how she came to be here; but she's very clear on one thing: the egg is the last offspring of a gold dragon who was her patron. She rescued the egg when the gold dragon was killed by a rival clan of black dragons, but she has no idea how she escaped their assault or where she's been in the intervening two centuries. A Knowledge (History) check can confirm that such a dragon existed and was killed by its enemies, but is this lady telling the truth? And if she is -- has the egg been tainted by whatever strange shadow magics brought it here?

- The darkness dissipates after a moment revealing a wyrmling umbral dragon, who is very surprised to be there and not happy about it. He wants his mommy. He's only five, after all. But at least these adventurers will make a tasty snack until Mommy finds him ... unless they win, in which case they have to worry about Mommy showing up and wanting to know what happened to Junior.

[SorrySleeping]

Scrapper wrote:

Fire Breathing Dire Bunnies...

May have to combine a few templates, but 3-4 critters of around CR 4, but scattered about the cave so they only encounter 1 at first, but hear the others in the distance, think Aliens...

Wrong reference.

Sunshine Rat! wrote:

Just use the real Demogorgon. It would be hilarious with a fifth level party.

I have an idea I'm stealing I think from reddit to start a Starfinder game when this one ends, but I don't think I'm ready yet to end this current campaign.