I came up with the dreamweb spider.
It's an ancient, immortal psionic spider made of crystal which steals, stores, and consumes its victims' dreams. The spider doesn't fight directly unless threatened, and prefers to attack when its victims are already asleep. It casts its dreamweb and leaves, ideally without waking its targets.
The thing that makes the spider really scary, both conceptually and mechanically, is that once the spider has stolen your dreams, you are unable to benefit from an extended rest until the spider is destroyed. Usually this results in the death of the victim from sheer exhaustion, but player characters stand a much better chance. Once a character's dreams have been taken, he has no choice but to hunt down the dreamweb spider, and fast.
The spider's lair is filled with solidified crystal webbing. Between every strand of webbing lies a dream that the spider has taken. Adventurers can touch these dreams to access their contents, but doing so sends a psionic impluse through the webbing and alerts the spider.
The dreamweb spider isn't very powerful in direct combat -- ideally, it should be fought after the players have been worn down by exhaustion. But, as a fun trick, when the spider is bloodied, it makes its attackers believe they've killed it, using the opportunity to become invisible and potentially flee. And when they finally do kill it, the attackers suffer the psychic pressure of every dream the spider has accumulated.
Let me know what you think. Too complicated? Too powerful? Not powerful enough? Should it be a higher level? Good concept/bad concept?
Here's a stat block! It's awfully big due to the complexity of the monster.
Reading your idea, I realised what you're trying to do here is two separate things. You need stats for your spider - and stats for the dreamweb, a hazard of appropriate level. You mention a desire for the spider to cast its web on a sleeping party, but you haven't given yourself a method to do this - the Dreamweb Strand requires the target to be taking ongoing damage, and that requires attacking a target, which will wake the characters of course.
So I took a swing at the concept - because I do like the idea of the creature very much.
Tactics: Dreamweb spider fights only when cornered and attempts to flee at every opportunity.
Dreamweb (Elite) Hazard
Level 13 Elite Obstacle XP 1600
Strands of translucent crystal spread across the ground, stretching from floor to ceiling and wall to wall, forming a vast shimmering web.
Hazard: This trap covers a 7-by-7-by-7-square area, filling it with a web of insubstantial psionic crystal. Creatures that begin their turn or enter spaces containing the web trigger an attack from the hazard.
Perception:
DC 19 an adjacent creature notices a shimmering disturbance in the air. The check can be made from further away at DC 24.
Arcana:
DC 24 a creature that can see the web identifies it for what it is.
Trigger:
When a creature begings its turn or enters a space containing the dreamweb, the hazard attacks.
Attack
Opportunity Action Melee 1
Targets: Each creature in a square containing the hazard
Attack: +20 vs. AC
Hit: Target falls unconcious and takes ongoing 5 psychic damage (save ends both)
Aftereffect: Target is immobilized until the end of its next turn.
Effect: Targets cannot gain the benefit of an extended rest until the dreamweb spider that crafted the hazard is reduced to 0 or fewer hitpoints.
Countermeasures
Insight DC 18: A character entering one of the hazard’s spaces can make a skill check to gain a +4 bonus to AC against the hazard’s attacks until the start of the character’s next turn.
A character can attack a space containing the dreamweb (AC 23, other defenses 18; hp 100; resist 5 psychic). Reducing the hazard’s hit points to 0 clears the webbing from the space attacked.
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If I was running this adventure, the final encounter being in the dreamweb spider's lair, I'd add a handful of appropriate level spiderling minions, reflavored for psychic damage instead of poison.
Also Note: the MB doesn't an action for something that takes longer than a standard action - thus the "short rest", the only other thing in the MB I could put there. I was thinking of the web as something like casting a ritual, taking about 5 min or so.
Your creature is very interesting, but it is over complicated and overpowered. Very overpowered. The lowest level monster I could find that could do 5d10 damage in any attack was a level 21 brute. You also have an at will interrupt (with no trigger requirement which means it could use it every round) that does 4d10. In one round the spider could do 8d10 damage to a single target in one round, and that poor character would also be dazed, immobilized, slowed, ongoing damage, and penalty to Will and saves. There are too many at-wills and some powers contradict themselves (Dreams of Victory at will + trigger when first bloodied should be an encounter power for example).
Reading your idea, I realised what you're trying to do here is two separate things. You need stats for your spider - and stats for the dreamweb, a hazard of appropriate level. You mention a desire for the spider to cast its web on a sleeping party, but you haven't given yourself a method to do this - the Dreamweb Strand requires the target to be taking ongoing damage, and that requires attacking a target, which will wake the characters of course.
So I took a swing at the concept - because I do like the idea of the creature very much.
[...]
Also Note: the MB doesn't an action for something that takes longer than a standard action - thus the "short rest", the only other thing in the MB I could put there. I was thinking of the web as something like casting a ritual, taking about 5 min or so.
Thanks for your input!
The reason it's overpowered is because I find that my group can handle almost anything I throw at them, and I prefer to increase damage rather than level because it's more exciting for the party to risk death from massive damage than to risk death because they can't hit the monster. I didn't consider how it would relate to other monsters of its level for that reason.
I quite like your revision, it makes things much simpler. I have a couple of comments.
By removing most of the web powers and keeping one as an encounter power, the spider can only fight in melee, which seems strange for a powerful psionic creature. I know that the dreamweb effect (no extended rest) is extremely powerful, but I do think the spider should have at least one at-will ranged option, or at least a recharge.
Relatedly, I still think the spider should have at least one attack that applies the unconscious condition, mostly for the purpose of springing the effects of the webbing on my party after they wake up from an extended rest. The spider wouldn't be able to create the dreamweb hazard if the party had a guard, so if the spider could sneak up and make the guard sleep, it would then be able to spin a dreamweb over the sleeping group.
Also, a sleeping creature wakes up when it takes damage, so I'm not sure about the ongoing damage on the hazard. If the spider created the hazard above a sleeping party, technically they would wake up as soon as they saved, rather than continuing their rest and waking up to find themselves encased in psionic webbing.
Keep in mind that Unconcious is not sleeping, it is a forced unconciousness and taking damage does not end a condition (unless taking damage is a requirement of ending that condition). I've fixed that now. Now, if a creature was sleeping when this dreamweb is dropped on them, you'll have two effects - a miss does nothing so the sleeping targert doesn't wake. A hit renders the target unconcious... so they're unconcious and taking damage and they don't know why and can't do anything about it except roll saves. Even when it makes it save its still immoblized and can be attacked by the dreamweb again on its next round. Its really quite a mean tactic.
Part of the thing is tactics, and based on what you described, here's what I imagined. The spider makes use of its invisibility to sneak up on the group. Invisibility doesn't end until it attacks, so it uses Fade Away to sneak up and wait patiently until it can get the most party members in a 7x7x7 square. It would also wait for its Fade Away ability to recharge before casting. Then it would cast out its web. It casts its dreamweb and gets the hell out of there. Technically with its invisibility it doesnt have to wait for everyone to be asleep, but the combination of darkness and sleeping people makes it easiest to get away after casting its web.
The spider has zero reason to stick arround and fight. If its lucky, the party hasn't even seen the creature, all they know is they have this dreamweb thing to deal with. After that they'd probably start looking around and asking questions. They could track the dreamweb spider back to its lair. The lair would have several, and the spider probably hanging out on the ceiling. This is where I'd also use the spiderling minions. The more the merrier.
I respect what you're saying about your group being powerful, so it easy enough to add dice to the damage.
edit: fixed a whole bunch of typos.