Mission from the frontline (session 35-38 or 48-51)

Dear Nori,
I heard your message loud and clear. Elturel is in danger. You're in danger. And I want to help you. But I couldn't. Not right away at least.
Like I told you before, we were “caught” by a devil bounty hunter. Not that we did anything wrong and came with him willingly, hoping to talk ourselves out of this mess. But before we could do that we had to sit in his warmachine for days. I mean, the Orthan stopped once to show us Zariels bridge (I’m pretty sure I heard that name before, but I can’t quite remember where). Apparently it's built on the site of an important battle. The furthest the demons ever came and Zariel got promoted back to archdevil after defeating them there. But after that break it was just one long ride to the frontlines.
Once we reached the frontlines we hoped to explain our mistake to Lucille, but that wasn’t possible. She either wasn’t there, or wasn’t available to meet the “ runaways.” We got signed up for the 667th regiment, which has a lot of humanoids. Once again, no choice here. The devil-shield has been suspiciously silent by the way. I think it means this army is not on his side and wonder if it means they are our allies.
Anyway, after a few days Fenrir and I got selected for a “special mission.” Which sounds like we made it, but it was mostly because our devil companions didn’t want to touch this mission with a stick. There were two more humanoids picked, Karen the Aarakocha, who is also from Elturel. She said her kid is a hellrider. I don’t understand how she got in this mess, but I decided to let rest. The other humanoid is a fire genasi named Roksana. She talked even less about her reasons to fight in the blood war. One other person was added to the special mission: Richard the bearded devil. I think Richard got added to make sure we wouldn't run away and report about the mission (somehow I feel like the devils don't trust our words as much as a devils’ report). However, Belforag, our amnitzu boss told him ‘he knows what he did.’ Which makes me very curious, but I never got an answer. The other curious thing about Richard is Fenrir's reaction towards him. I mean, Fenrir didn't say anything, but his face said a lot. Mostly that he knew Richard. I'm pretty sure devils can't keep their memories from their mortal lives, and I don't want to give Richard the tools to torture Fenrir, so I haven't asked him yet.
Anyway, our special mission was to figure out what happened with the 669th regiment. Apparently they lost contact. They already sent a few more devils towards them, but those never returned. Their last known location was at this big hole filled with water. Luckily for us the water isn't Styx water, so we don't lose our memories if we touch it. That would have been a real problem.
Anyway, when we arrived at the hole, we saw the devils right away. At first, we moved very stealthily, making sure the devils wouldn't see us. But then we realised they weren't moving. We got less stealthy. They weren't moving. We stood in front of them. They weren't moving. Then Richard grappled one of them. They started moving. And attacking us, which somehow still got us by surprise. It was a pretty hard fight, mostly because we weren't as much fighting the devils as an apparition of an aboleth. Reileth, as the monster was called, mind controlled the devils. The only way we could wake them up was by hitting them until they regained their senses. Literally. Thing is, we didn't want to kill the devils, but wake them up since more allies means better chances. And we couldn't hit Reileth since it wasn't really there. It also made illusions of more enemies like we weren't attacked by half an army. And Richard got under its influence as well. Like I said, it was a tough fight, but in the end we woke up most devils.
Feeling hurt and not ready to face Reileth for real yet, we went to the devils’ base. We ate and slept there, although Reileth kept appearing out of a bucket of water. That's probably how it got the 669th under its spell in the first place. Richard told us the mission wasn't done until we killed Reileth. So, the next morning we went back to the hole.
We drank the potions of water breathing and dove into the water. The hole was pretty deep, but eventually we found a side cavern. The side cavern had an air pocket filled with devils and humanoids. I thought (and quite frankly, still think) it was the monster's pantry. However, we didn't see a big beast, so we went back into the water to find it. Deeper in the hole we found some kind of underwater lake (weird, right?) filled with some thick corrosive liquid. Not wanting to go through the thick muck, we went back to the air pocket, hoping to find some clues about where Reileth was. We didn't find any clues, but we did find the monster itself. I still don't understand how something that big can hide that well. The devils and humanoids were, of course, under its control so it was once again one massive battle. Except now we were actually fighting the monster. And the humanoids weren't humanoids but weird fish-tentacle people in humanoid disguise. Karen managed to banish Reileth at a certain point, but unfortunately the mind controlled devils kept attacking her so she had to drop it at a certain point, bringing Reileth back to our fight. Roksana had summoned a powerful elemental, but the devils made her lose control over it. Fenrir and Richard, who hadn't had the chance to get out of the water, kept being attacked by Reileth. Their stamina was being challenged, but they persevered. Despite the odds, we got Reileth to flee. After we awakened the devils and defeated the fish monsters we took some healing potions and started the pursuit. Actually, I feel a bit guilty about this. I kinda pushed the party to move on without realising how injured they were. We brought the devils as well, by the way. More targets for the monster.
The side cavern didn't have any other corridors or exits, so we went back to the underwater lake. Karen blessed Fenrir so the acid wouldn't hurt as much, and he dived into the muck. I sent a message to him, to figure out if he had seen Reileth. When I didn't get an answer I panicked and went in after him. I couldn't see in the muck, the water breathing didn't work and the muck hurt my skin. I think everyone else followed me, probably thinking Fenrir had found the monster. Which he technically speaking had. We just couldn't see it. So we had a hard fight in water that hurt our skin while we couldn't see. While we were in there all I could think was how we had to get out of that stuff. So I grabbed Reileth and dragged it out of the acid. It really did not like me dragging its ass out of the muck so it kept attacking me (which might have been a good thing considering my companions didn't feel so well). Once I could see what I was doing I grabbed the tentacle that was coming in for an attack and strangled him with it.
After we defeated the monster and tried to go out of the water we learned Karen and Richard were sick. They have to stay wet. It was really hard to not tell Karen she was basically a duck now, but that would be mean, especially considering she cured me from the same fate. Back at the 667th we didn't get a reward or anything. However, they did tell Fenrir and me we got a new mission. In Elturel! So I'm going to you! I imagine I'll be there fast too, considering all the war machines and magic they (probably) have.
Stay strong,
Your loving sister,
Caja