Reading through the module, the following points stand out to me:
- As written, this is a very combat oriented module. Did anyone find a way to break up the long dungeon crawl with good roleplaying opportunities?
- The 'getting to Icehome' skill challenge needs to be redone to give a feel of an actual challenge rather than a series of rolls.
- The apparatus is not suitable for combat (+5 vs. AC will never connect with an at-level enemy, and will frustrate players. Despite the reference to 'encountering a patrol of sahuagin,' it's not viable as presented in the module.
- How did Chillreaver work? I worry about solos being uninteresting combat, even when coupled with a trap.
- Are there any tie-ins to future modules I should make sure are worked in?
- My group is about half way through 'Haven of the Bitter Glass'; is there anything I should make sure is worked in for this module?
I do plan on updating damage based on the latest errata, so I expect the encounters will stay threatening as written.
The apparatus skill challenge was a case of awesome idea/horrible execution IMO. Honestly I think it'd be awesome if you had them be attacked by Sahuagin or something along the way, and if the apaaratuses take too much damage... not good. Maybe throw a bunch of minions at the heroes, who have to work together in pairs to make their moves and attacks.
Yeah definitely give the apparatuses different stats. Maybe give them a base plus to hit equal to the PCs to hit bonus, and then people trained in arcana and/or dungeoneering get an extra +2 to hit.
Chillreaver worked pretty well, except at that point in the game i had a bard in the group who was pulling some goofy tricks. Mantle of Unity was disruptive, and then he had this power combo where whenever Chillreaver attacked them, the party healed, and whenever Chillreaver missed the party, they gained temporary hit points. Aside from that, I'd suggest doubling Chillreaver's static damage to make him more of a threat, though you sound like you're on top of that.
The nastiest thing is that he has threatening reach and with his opportunity attack he can push you back! He really frustrated my melee guys.
As for tie-ins... Chillreaver is one of Tiamat's exarchs along with Virizan (green), Vraxanault (red), Mornujhar (black) and Namissi (blue). You could throw in a nod to them somehow. And as mentioned, the devas of Nefelus can become a very powerful ally in the war against the githyanki.
The Seed of Winter is part of the Stone-Skinned King adventure. The Seed belongs to a winter fey spirit called Inzira. She will want it back. But she will want your heroes to use it to tempt Cachlain, the fomorian, to join your cause.
As for tie-ins with Haven, maybe have talk of Nefelus getting sealed off at the party at Lord Telicanthus'? Or maybe a deva who lived in Nefelus is at the party and speaks of her homeland?
The nastiest thing is that he has threatening reach and with his opportunity attack he can push you back! He really frustrated my melee guys.
he pulls not pushes per adventure stat block. push would have been more entertaining pull mostly hurt squishies once he got to them.
personally i found the trap attack roll too high, highest will in my group was 28 and despite one player basically volunteering to sit there dominated it was still a major pain in the butt.
when you save against that you become immobilised meaning you're stuck there again for next rounds dominate attack.
also poor party tactics were implemented, one pc died, seed was knocked off plinth, iceberg started to collapse and so chillreaver fled with stone. he had 226hps at this point and had used the 2 surges provided by the arcane dais (party also used this 3-5 times)
nobody in party could read draconic and so they went the other way in.
maybe this was all just bad luck...
As for the apparati of Kwalish stuff, I'm going to look into modifying this skill challenge, much as I did the Green Dragon Inn scene in Beyond the Mottled Tower. It should be much more active and tactical than it is.
Also, with regards to roleplaying in Icehome, encountering Uarion has the makings of an interesting roleplaying encounter. As written, you save him by beating him unconscious. Perhaps a skill challenge during the fight, with appropriate skill checks used to try to help him break free of the mental domination.
I like this. It occurs to me that the Frost Giant leader might also 'negotiate', and perhaps a Sahaguin representative as well. Each might give ominious details about the impending danger facing the island.
As for the apparati of Kwalish stuff, I'm going to look into modifying this skill challenge, much as I did the Green Dragon Inn scene in Beyond the Mottled Tower. It should be much more active and tactical than it is.
If you get a chance, I'd be interested in what you come up with. I'm not quite sure how to make it tactical, but I'm brainstorming adding problems (ice floes, rough waters, sea creatures converted to frost creatures) that they have to deal with. Nature might be necessary to know how to bypass the creatures without arousing them, etc.
In fact, the adventure suggests that Nara sell out Chillreaver to save her own frozen skin. I'd have her negotiate for her freedom once she's bloodied and she's lost a few of her allies. The winter wolves can die without any real problems, but if too many of her giant allies get killed, she's pragmatic enough to turn against Chillreaver. Anyone that can challenge this much of Icehome is a force to be reckoned with, and can probably challenge Chillreaver in his lair. As for the sahuagin, I doubt he'd surrender - the sharkmen are pretty predatory, and surrender is probably anathema to them. Kill or be killed, and all that.
Looking into the Kwalish section, the way I see it, the encounter is about sneaking into Icehome. The adventure gives four skills that offer successes. It's put together pretty poorly, so scrapping it's probably your best option. This should feel like D&D meets Metal Gear Solid - one of the good ones, where Solid Snake could actually finish his own games - with equal parts skulking about and action. It should probably be an encounter where the party starts on one side of a map, and need to get to the other side. There's lots of sahuagin in the way, as well as giant sharks and other frozen deep sea horrors, and in order to make it across they need to draw some of the guards away into a secluded area and kill them to open up a chink in Icehome's perimeter.
You're right about one thing, the +5 will never connect, but fortunately there's a bit that the pilot can add half their level to the attack roll. That should be about a +12 at this level; still not great, since the guards have a 27. I'd give the copilot an attempt to pull some levers and assist with the attack, granting a +2 to attack that should make things about right. Arcana, Dungeoneering and Thievery all sound appropriate to trying to figure out how to make the lobster mecha work. I'll look into creating some sort of map with hazards - icekelp, coral reefs, rough water and so on - and see what I can do to make it an interesting encounter. 
I was thinking of having the PCs roll some checks at the beginning to figure out how to drive and control it. Successes on these checks would give a +2 to hit in combat with the Apparatus or a +2 to Driving checks.
I like the idea of a combat encounter where the PCs have to get from one side of the map to the other. Maybe it's an underwater chasm they must traverse to get to the entrance of Icehome? Good spot for ambushes, etc. I like the idea of minion sahuagin and then maybe a solo or elite sea monster in the middle.
During combat, one PC drives while the other makes attacks. Driving across the terrain during combat is a Move action with a hard DC check to maintain stability over tough terrain. Success means you arrive at your move action destination. Failure means the Apparatus makes it there but falls prone. This should give the Driver stuff to do during combat. I also gave the Apparatus an encounter power move action (Release Jets) that allows it to move up to twice its speed.
I think terrain hazards like whirlpools, strangling kelp, etc. would be cool too. With the clash of warm and cold water, I'm sure the currents would be pretty strong here.
Any thoughts? What did you do to spice up this encounter?