No it disengaged as a BA so no opportunity attacks.

(Should we wait for Deva to move the light before attacking blindly?)

Within the chaos of the fight, Devarus eventually finds a moment to draw a longbow. By then the creature had already scuttled off into the darkness. "Quickly! Before it escapes again!" He called as he took out one of the enchanted arrows and loosely lined up a shot. By his will alone the floating orbs dance their way after the creature, leaving the group in darkness, but showing the way.

The moment he spies the creature while following along after his orbs arrow after enchanted arrow flies. And if even one hits, he calls out "Now Ruu!", bridging in that moment both Hunter(Ruu) and Prey(Farmer Boy) with both words and key, draining the spirit of one and infusing it into the other for a brief moment.

Bonus Action: Move Dancing Lights up to 60ft, or until creature is visible along with a space behind it and in front of it.
(ie: *  *  C*  *, in *=Light Source and C=Creature)

Movement: 30ft closer towards the Farmer Boy.

Action: Attack w/ Longbow and +1 Arrows.
#1To Hit: 18 For: 7 magical piercing damage.
#2 To Hit: 8 For: 6 magical piercing damage.

(If hit by either, expending last superiority die for Maneuvering Attack Maneuver, dealing 8 additional damage and granting Runt movement as her reaction(if she chooses).

(Whoops. Forgot to change the damage die for the attacks. Here are the corrections:)
(#1: 13 + Crit Damage for Maneuver: 6. (-2 off crit bonus)
(Total Damage: 32.)

Devarus positions the wisps in the correct positions to take aim. He takes aim alright. He releases a single arrow with more than enough destructive potential to cripple the creature. It hits the metal leg and causes it to break. The creature crashes in to the dirty water, splashing the party. The creature falls on its own sickles, impaling itself. With a earth-shaking howl, the foul abomination finally dies. The sounds of loud boom reverberates through the house. Two more Hex Foci hidden somewhere in the large labyrinthine mansion are detonated with the creature's death.

The mansion grows quiet. The only ambient noise is the dripping of water. The party feels an evil presence being lifted from this place.

Battle Victory.

Everyone gets 1,500 XP (I will add it to your sheet)

“Anyone else in need of a shower and a beer?”

Runt will try to take one of its scythe arm things as a trophy.

Runt grunts in agreement with Genden.

Most of the Affectus Uti from the Sickles have washed away leaving behind a residual magic aura.

Runt gets two Sickle+1s

"Not yet." Elsara says. "There's possibly something left over that was the root cause of the Affectus Uti. I wanna go check the building again." She tells the others. "If there's something left behind here, it could end up happening again, but with someone else."

Runt straps the two sickles to her weapons belt, in addition to all her other weapons, increasing her passive intimidation factor. In her mind atleast. A relatively petite half orc needs to be scary in somefashion, might aswell be covered in weapons she took from fallen foes.

With this creature dead, other totems probably broken now. May need to check for them to make sure.

“Well, you’re not searching the house without me.” Gendan accompanies Elsara as she scans the rest of the house for residual magic. 

Devarus chuckle in response trailed off naturally into a sigh of relief. "That certainly was far closer than this one expected.. but I do agree. Someone should see to Val though just in case. Even with the beast dead, this Affectus Ulti has been proven to be a rather tenacious "beast" to be rid of for sure." He said, and would perhaps be the first to double check the elf's wounds just to make sure he hadn't suffered as Dev before.

Medicine: 14.

With that eventually out of the way, Dev takes point with the intention of heading right for the library again.

Affectus Uti is strong and hard to get rid of. Luckily Val isn't bleeding out like Deva was but it's clear that it would take a Lesser Restoration spell to allow Val to actually heal his wounds. (Still can't recover HP)

Heading back to the library, the darkness has completely vanished. Now there is only regular darkness which is natural and can easily be seen through via dark vision. On the north end of the library is a door locked with a heavy padlock. A key that you found first time when you searched the library's floor unlocks the door. Beyond appears to be a small personal study. The books here seem to be in much better condition. There is a desk here with a few sets of drawers. I bottle of ink sits on top of it though it has long since dried up. On a corner is some shattered bones and broken candles. Looks like you found the location of a 2nd Hex Focus. This one was destroyed when the creature was killed.

Elsara will collect the pieces of the other focus, wrapping them in her spare blanket to place within her backpack of holding so they can look at them later for further research.

Elsara does that. What does the others do?

Devarus focuses on searching the drawers themselves. Out of consideration for its previous owner, he is mindful enough to make sure there weren't any traps while working, though the mind wouldn't be far from Valwaryn. He silently hoped that the elf may yet find some measure of rest. If not, their venture may yet have to be cut short. Even if granted they discovered the source of what had been troubling the grasslands.

Trap Search: 8.

Search for any Useful Documents: 7.

The drawers weren't trapped an only had one document so even if you rolled a 1 to find useful things, you still would have found it.

The document in question is a diary. It seems to have belonged to Aron's great grandfather.

Gendan is interested in shiny objects that might be good for bartering.

Investigation 14

Unfortunately Gendan can't find any good shines. ((Why is everyone rolling a 4?))

Runt is also interested in shinys good for bartering 

Investigation 15

(Awe, I broke the streak of 4s)

Runt manages to pick up various expensive paperweights. They are essentially useless to the party but they are worth a total of 180 GP