So I've finished running my group through Dark Pursuits and Desolation of the Dead so far.

First of all: In Long-las we trust. Seriously, Accurate might be a bit too powerful, I don't really see the point of other single shot weapons (that aren't super rare/unsubtle) when you have these things.

The Daemonhost...blew itself up with perils of the warp while fighting the Heretek (who blew the PCs out of the water when it came to DOS to locate the host) and his servitors. The Heretek got sniped in the back of the head and had to burn fate before that. I rolled Annihilation (which I didn't have kill him, because A) he's needed for Forgotten Gods and B) he's a Daemon) and then I ruled that this spawned a Lord of Change. Said Daemon went to the main port (after the PCs fainted cause Fear (4) and it dusted the remaining servitors narratively) and had to be stopped with orbital bombardment, which the PCs just managed to outrun. Then, in a rather impressive bit of scheming, managed to blame the entire episode on the Heretek while covering up their own presence more or less entirely (their Inquisitor did the rest, and had the captain he ordered to destroy the port executed just to make sure).

The Herald of Nurgle went down in two Long-las shots but the sniper didn't have a easy go at it. First of all, they managed to recruit Vornas and his gang (they saved the town and impressed him earlier in his games). They also conscripted some of the Sanctionaries, who were doing penance for arresting them earlier before they found out they just hauled in a bunch of Acolytes (Oath-Captain Nils executed the grunt responsible on the spot). During an earlier shootout with the cult, one of the PCs had to burn fate after he took a bunch of autogun bursts (totaling about 9 critical damage) and then he decided that since his character would be bedridden for weeks he'd run a reinforcement character. So we had a SoB Canoness in the party (pretty brutal, but by far the least nutty RC given, we are making more reasonable ones for later) which definitely helped. They also conscripted a bunch of mutants and used them as anti-cult cannon fodder (through a bunch of amazing Command and Charm checks on the party of the Seeker, who also told the Sanctionaries to shut up and sit down about the gang, as well as telling them that they were screwed by the cult if the didn't help, cause zombies).

The cult troops went down pretty hard, the mutants soaked up bullets for the first few waves, while the Sister and the gang just stormed their barriers and killed about half of them while the rest fell back to the main chamber. Round One: Fayne only avoids long-las death because one of his minions dodged into the bullet (I figure crazy cultists should have a rule like Look out, Sir! from the table top). Cultists and the misfit band exchange fire and not much happens. Round two: Fayne takes a long-las shot blowing off his leg after his ablative armor cultists are dispersed by the Sister's grenades, and has to burn fate to avoid death. The Herald is spawned and pretty miraculously, the cops and the gangers all pass the fear check (I did it collectively cause screw roll for like 15 troops NPCs). So does the Sister and the Seeker, but not the Sniper, who is stunned for a round. Herald attempts to cast Nurgle's Rot and fails the focus test. Sister uses her anti-corruption FOE fate ability to wipe out the cultists or close to it and nick the Herald. Dead start rising, meaning the NPCs now have their hands full. Sniper manages to snap out of it after that round. Round 3: Long-las hits Herald, knocking off about 20 of its wounds on a good hit. Sister finishes off remaining mooks. Herald is unhappy about this and tries to club the guy with the nasty gun, but then the Seeker gets in between them and takes a club to the chest, going down on 6 critical damage (just avoiding death). Herald takes 3 wounds from Vornas and Nils shooting it. Round 4: Another good long-las hit sends the Herald back to the Warp. Seekers ribcage is still destroyed.

So yeah, Long-las eats everything and my iffy rolling with the Herald definitely helped them (as did their roleplaying and recruiting allies), but without that gun they probably would have been slaughtered. And they even managed to take Fayne alive for bonus experience, though Nils and co aren't exactly happy with them but they have no intention of messing with the big I.

RationalInsanity, I'm impressed at how you kept that on track! It sounded like great fun!

But I don't think that Daemonic psykers can actually be affected by perils they generate (or is that only in Black Crusade?).

Daemonic psykers are affected by perils, just not psychic phenomena. Trust me, I double checked when it went down.

And had the Herald gotten off Nurgle's Rot, things would have been very different. That could have turned the gangers and cops into Plaguebearers, had it killed them.

I also found that the corpses were essentially useless against characters with decent toughness and armor (their max damage is 8 and zero pen, and they don't even have toxic backing that up), so I used a group mechanic to have multiple ones swarm the PCs and up their damage to 1d10+5.

As a first-time player I was stunned when we engaged Suvfaeras in Dark Pursuits... even in a weakened state our gear/skill/attributes paled in comparison to the Daemonhost, despite the Heretek and his men.

It took a missile and good few frag grenades to put it down.. I missed with the first few missiles as I had no training in said weapon. Meanwhile the Assassin was attempting to put out the burning Chirurgeon, the IG was in shock from a failed fear test, the only other character who was up was plinking away with a stub revolver... eventually the IG stepped in and added his heavy stubber to the mix!

We are about to begin Desolation of the Dead, I dread to think what awaits.

When in doubt, if the players know they'll be facing a daemonic entity, blessed weapons are a great solution. Even if the blessings are temporary (say, one encounter only), if you can get through the boss's daemonic protections, then it makes things far less one-sided.