Aquatic Aberration help

[Chilxius]

My players are going to be taking out a cult soon, and because of the nature of my campaign I want there to be an aberration as the boss monster, and preferably an aquatic one. The best I've found so far is the Chuul. The problem is that the party will only be ECL 5 at the time, and there are only three party members:
Warforged Fighter
Human Wizard/Warmage (Ultimate Magus)
Mermaid Shugenja (NPC)

Can this party take a CR 7 Chuul?
If not, what about the Gauth? (Lesser Beholder)

[Thurbane]

Ixitxachitl with class levels (say, Cleric) can be pretty sweet, and present a real threat to a party. Vampriric Ixitxachitl get energy drain attacks.

The biggest problem with boss encounters is action economy, so might be best to give whatever creature you use a few minions as well. Swift and Imnmediate casting time spells help a little with the action economy issue, but not as much as more creatures on his side.

Against a party of 3, though, this shouldn't be as much of an issue.

[DrMotives]

I second Thurbane's suggestion. Also, not only are ixitxachitl social monsters that live in communities, the cleric has plenty of baked-in minionmancy powers. It's also the standard class for them.

[Chilxius]

You guys are right - ixitxachitls are exactly what I was asking for. Problem is I've already used them; they were the first things my characters fought, except for the Kuo-Toa slaves the ixitxachitls were controlling. I'm using the Leviathan Elder Evil for my campaign, so I introduced ixitxachitls early since they play a major role in the Leviathan's plot. I also want my players to have some experience fighting aberrations so that, when the Aspects of Leviathan start to appear, they have some tools to deal with it.Ixitxachitls will be popping up very often in this campaign because, as you said, they are pretty sweet aquatic villains.

Since reading my earlier post, I've remembered that Warforged are immune to paralysis. That makes one of the Chuul's biggest threats obsolete, so that will probably be my boss monster. And maybe some sharks. Never hurts to throw in more sharks.

[Andion Isurand]

What about anguillians from stormwrack?... lawful evil medium-sized eel-like aberrations with limbs for using weapons and such, which means more loot options... plus they can move a bit out of the water.

they start at CR 2 and advance by character class

[ShurikVch]

There are some other aquatic Aberrations:
Skum (http://www.d20srd.org/srd/monsters/skum.htm) CR 2
Tako (Oriental Adventures) CR 3
Morkoth (Monster Manual II) CR 5
Ahuizotl (Fiend Folio) CR 6

Also, from Dragon magazines:
Opabinia (#348) CR 2
Grindylow (#352) sorcerer casting; CR 6

[Segev]

I was going to make the to-me obvious suggestion of an Aboleth, but if you're worried about a CR 7 Chuul, a CR 8+ Aboleth is probably not a good plan.

A Gibbering Mouther is a CR 5 aberration. Slapping the Aquatic subtype on it wouldn't really change much, except letting it be something like "whispering water" or something.

[Chilxius]

Yeah, we'll be fighting Aboleths, but not yet. That's for later, when things really start to get going. The skums will come in then too, since they're Aboleth slaves. Just looking at the Aboleth's enslave-three-creatures-a-day ability, I can see my whole party getting ended in three rounds.

Morkoth is good. Morkoth is very good. I'll be using that later. That'd be good for a "oh no, where did our teammate go" situation, or just as a "ahh what is that kill it kill it".

Ahuizotl is will be good for a roadside encounter. It or the Morkoth would work well for a town with people who keep disappearing. Aboleth works well for that too. In fact, I like the idea of "we killed the Ahuizotl; why are people still disappearing?" and the Aboleth was the real threat all along.

Anguillians could be good villains, but I think they'd be a good one-off challenge. Maybe if my PC's have to escort some huge friendly sea creature, then these tooth-heads come in and all latch on and start sucking the life out of it.

This is all great help. I'm getting ideas just looking at these monsters. I'm hoping to throw aberrations at them enough that they start investing in aberration-bane equipment, or equipment/spells/classes from Lords of Madness.

Let me also take the time to say WHO NAMED THESE THINGS? Ahuizotl? Zeugalak? Otyugh? Did you sneeze while naming these? Ixitxachitl? I can't spell that! I can't even say that. I literally copied-and-pasted it just now.

[DrMotives]

Let me also take the time to say WHO NAMED THESE THINGS? Ahuizotl? Zeugalak? Otyugh? Did you sneeze while naming these? Ixitxachitl? I can't spell that! I can't even say that. I literally copied-and-pasted it just now.

Only one of those I can speak to is the Ahuizotl. That's a demonic servant of the water god from Aztec mythology. People would be ritually drowned to death to appease the god, and the ahuizotl would come and eat the waterlogged corpses.

[Extra Anchovies]

Monster Manual 2 has some nice stuff.

Darktentacles (CR 7): basically the Watcher in the Water, but a lot smaller.
Kopru (CR 6): weird aquatic dwelling things that used to be highly civilized. Sorta like a headless mermaid with a big scary face in the middle of its chest. They like to grapple.
Morkoth (CR 5): fish-octopus thing that lures people to their deaths with a hypnosis ability

Those are the aquatic-y ones, along with the aforementioned Ixitxachitl.