A little while back my party took care of some rust monsters in a mine near their base. During the fight someone made a comment that they probably had a nest with a queen like in Aliens. It was funny and the party was both excited and terrified of the prospect. So, like a good DM, I am stealing that idea and building an encounter for them to have to hunt down and take out the queen! I can probably just scale up a rust monster if I have too, but I was looking to see if there are any good existing monsters that would be similar to that type of xenomorph-esque queen that I could repurpose.

I've been going through the monster list and nothing is really striking me, so wanted to get some second opinions on what others would use for something like that.

I'm not too worried about CR because I don't know exactly when they will find their way back home (they are off on an extended adventure at the moment) so I'll need to scale it up or down depending on where they are at level wise by then but they are a group of 7 level 7 players now, and I would guess they will probably be about level 10 by the time they make their way back to their base, if things go like they seem to be, so it will definitely need to be a decently challenging monster.

I definitely want something with some lair actions and maybe even a minor regional effect localized to the cave where the nest is of some kind if there something that would make sense.

So, hit me with your best ideas, what would you use as a base monster to make a xenomo... um, i mean, rust monster queen?

closest thing is maybe an aboleth? idk but its a cool idea. i made a monster called the thing in the dark and it might work

Captain Crunch is correct.  The aboleth can make for a very good version of the underwater aliens from Alien: Resurrection.

My top contender at the moment is the Deep Dragon, I would just modify its breath weapon and spores etc to a corrosive type effect.

Quote from Mog_Dracov >>

Captain Crunch is correct.  The aboleth can make for a very good version of the underwater aliens from Alien: Resurrection.

 

 Aboleth could work. I had been thinking more of a lair in an overrun dwarven mining outpost that they gorged on all the accumulated metal, but I could make it a subterranean lake for a twist. 

Have you considered something like a Kruthik Hive Lord? It has a very alien design and its acid spray can be tinkered with to simulate a stronger version of a rust monster's antenna. Or you could just staple that and the Rust Meal abilities on and have a rather dangerous beast at ~CR5-7.

Quote from Metamongoose >>

Have you considered something like a Kruthik Hive Lord? It has a very alien design and its acid spray can be tinkered with to simulate a stronger version of a rust monster's antenna. Or you could just staple that and the Rust Meal abilities on and have a rather dangerous beast at ~CR5-7.

 Oh thats a good one!

I recommend something custom. 

Pick a base like the [Tooltip Not Found] or if you have the new book there is the ruin spider. then add  a stronger version of the antennae attack  by looking to  like the ruin spiders ruin bite or the black pudding's pseudopod  attack.  It could also be worth adding the corrosion effect to the hive lord's spray attack.

Then add legendary actions and lair actions  

For regional effects try

• pools of acid
• Tunnels and maybe sink holes

for lair actions try 

• Summon 1d4  young kruthics hatch from an egg 
• Part of the ceiling collapses. Target dex save or damage and restrained  and creating difficult terrain
• Sudden hole, save or fall down a hole that opens up 

You could possibly consider combos like the the lair actions with ceiling collapses and holes in the ground are more coming. 

For legendary actions probably just take the classic move and bite options. 

Quote from Hawkeye83 >>

A little while back my party took care of some rust monsters in a mine near their base. During the fight someone made a comment that they probably had a nest with a queen like in Aliens. It was funny and the party was both excited and terrified of the prospect. So, like a good DM, I am stealing that idea and building an encounter for them to have to hunt down and take out the queen! I can probably just scale up a rust monster if I have too, but I was looking to see if there are any good existing monsters that would be similar to that type of xenomorph-esque queen that I could repurpose.

I've been going through the monster list and nothing is really striking me, so wanted to get some second opinions on what others would use for something like that.

I'm not too worried about CR because I don't know exactly when they will find their way back home (they are off on an extended adventure at the moment) so I'll need to scale it up or down depending on where they are at level wise by then but they are a group of 7 level 7 players now, and I would guess they will probably be about level 10 by the time they make their way back to their base, if things go like they seem to be, so it will definitely need to be a decently challenging monster.

I definitely want something with some lair actions and maybe even a minor regional effect localized to the cave where the nest is of some kind if there something that would make sense.

So, hit me with your best ideas, what would you use as a base monster to make a xenomo... um, i mean, rust monster queen?

 

Rather than Aliens, you could use the OG Star Trek episode with the Horta for inspiration if your campaign would fit that sort of thing. Maybe the rust monsters are out hunting for iron because their nest was built in an area with large quantities of things they can't eat (i.e. precious gems). Finding a way to communicate with the queen rather than fighting her could end up being a win-win for everyone, even the miners

If it does come down to a fight, I think you'd be fine scaling up a normal rust monster and putting a twist on its abilities. Maybe in addition to rusting metal, the queen has some sort of magnetic pull to bring metals closer to her -- dragging along the poor sap wearing or carrying them...