3-phase boss monster: cranium rat hive mind

[Quickleaf]

I'm going to throw a boss monster at my players next game - a cranium rat hive mind. The fight is going to be in 3 phases, following AngryDM's pointers. Any feedback on the basic setup or the stat block details is much appreciated. I've attached the stat blocks as image files.

The setup is the PCs* are trying to reach a portal down in the sewers of Sigil. They've just prevented an assassination attempt that was in part orchestrated by the cranium rats, so they've got a bit of a bone to pick. Negotiation is possible, violence is probable.

* Four 6th level PCs with all roles covered.

PHASE ONE: "Hide and Seek"
There is a large sewer chamber with sewer water running down the middle; at each corner are platforms elevated 20' off the ground floor. Higher up are older alcoves and caged sprites. The hive mind and 4 cranium rat minions are within. During this phase the hive mind acts partially like a skirmisher/artillery, sneaking from platform to platform to unleash spells at the PCs.

PHASE TWO: "The Swarm"
The hive mind scatters and is removed from play (all conditions on it end) and 12+ cranium rats are summoned. When half the rats are defeated the hive mind returns in any square, and makes the following gaze attack vs. all enemies: +10 vs. Will; trapped in Vishkar’s Nightmare until PHASE THREE or escape. During the rest of the phase the hive mind attacks in melee using the cranium rats to its advantage.

The Vishkar's Nightmare is a complex lethal illusion puzzle. While within the nightmare, PCs aren't subject to attack from the hive mind and cranium rats. If they don't escape by PHASE THREE, they are turned into cranium rats and dominated (save ends both). If they escape in time, they gain a small bonus.

PHASE THREE: Evil Emanations
The true horrific nature of the hive mind is revealed as it levitates off the ground, drawing cranium rats that don't flee into it like a gravity well (all conditions on it end). Hovering at the center of chamber as a swarm of whirling rats it vaguely takes on the shape of a rat's face with wraithly red eyes. A wave of foul energy pulses outward in a close burst 10; Attack +10 vs. Fortitude (ignore cover & concealment); Hit: 1d10+7 force/psychic damage and prone.

That's what I've got so far! How do you think this will stack up? Too hard?

 

[the Jester]

At a glance:

It seems to have too many hit points. As a swarm, if anything, I'd reduce its hps from standard, not increase them.

The immediate reaction where every adjacent ally attacks an enemy that attacks the hive mind seems a bit much too.

 

[Quickleaf]

At a glance:

It seems to have too many hit points. As a swarm, if anything, I'd reduce its hps from standard, not increase them.

Makes sense. But I'm torn whether or not to house rule swarms in regards to the "half damage from melee/ranged attacks". If a melee/ranged attack can daze or knock prone a swarm, how do I justify it doing less damage? Maybe instead the swarm could "outsource" an amount of melee/ranged damage to cranium rats like it can do with conditions?

The immediate reaction where every adjacent ally attacks an enemy that attacks the hive mind seems a bit much too.

It triggers off of opportunity attacks and as an immediate reaction happens only once per round. Still maybe it's too powerful? What if I limit it to one adjacent cranium rat attacks the PC making an OA against the hive mind?

Thanks for the comments.

 

[the Jester]

Makes sense. But I'm torn whether or not to house rule swarms in regards to the "half damage from melee/ranged attacks". If a melee/ranged attack can daze or knock prone a swarm, how do I justify it doing less damage? Maybe instead the swarm could "outsource" an amount of melee/ranged damage to cranium rats like it can do with conditions?

Without a compelling reason to change the swarm mechanics, I wouldn't do so. I'd leave them as is on this.

It triggers off of opportunity attacks and as an immediate reaction happens only once per round. Still maybe it's too powerful? What if I limit it to one adjacent cranium rat attacks the PC making an OA against the hive mind?.

Then I think it's just fine. You could probably even make it an opportunity action so that it could trigger 1/turn instead of only 1/round; then instead of "EVERYONE BITE THAT GUY!!" it becomes "EVERYONE GUARD ME!!"

 

[Quickleaf]

Well we've started this encounter with a complex 3-D sewer map (I'll post a picture when we next get together). it's kicking the PCs' butts and we haven't even finished the first phase yet! Already they're considering a tactical retreat...only problem is getting an extended rest is going to be difficult since they're kind of trapped in the sewers by a pocket of methane gas and there are lots of cranium rats & wererats eager to give pursuit.

I chalk the difficulty up to a series of bad rolls and the lurker qualities of the hive mind which is exploiting the 3-D terrain for maximum advantage. Also, I included 16 cranium rats at the encounter's start, though they only attacked if attacked by the PCs first.

I've been surprised by how dangerous the hive mind has been, especially because most of the PCs (minus the cavalier) have close blast/area burst attacks.

 

[Quickleaf]

EDIT: duplicate post, delete