In a world where Napoleon's soldiers have been turned into undead monsters, and purple goo has completely decimated monumental structures, it's quite impressive that Valor Mortis finds a way to add new layers of weird to proceedings.
The quest 'The Curious Case of Sheamus Diggory' is one such oddity, as you come across a man living in a shed secluded from the madness that has befallen the Cursed Hollow. He's unwilling to go out in the sunlight, and he's asking you to get him some blood. No brownie points for guessing what his big secret is.
Here's how to handle this quest, and what you should do about the big decision at the end.
Locating Sheamus Diggory In Valor Mortis

First of all, you'll need to find this sanguine creature hiding out in his dingy shed. To do this, you'll need to get right to the end of chapter six, to the section where you need to platform across the water using debris floating downstream. The loop back to the building where you get the Claymore leads downstream, but you'll want to go against the flow and use the grapple points to get to the other side of the stream on the right.
Do this, and you'll be able to talk to Sheamus through the window of his home, and he will ask you to gather some untainted blood.
Finding Blood & Wine

To begin with, you'll need to navigate the fields behind Sheamus's home, which is filled with explosives and explosive enemies. Have a pistol out and be ready to pick off anything that runs at you from range. Steadily work your way to a door at the back of the field, and this will take you through to the mini-boss arena.
This area is guarded by a boss variant of the Howler, and this one has more bite than most. Essentially, it's got a much beefier HP bar, and it can also spawn temporary dog companions to swarm you. In short, it's a nightmare.

What I would suggest for this fight is having as much ammo as you can for your blunderbuss, and then I would suggest pumping the main enemy full of pistol bullets from as far away as possible while using dodge to evade the other summoned dogs. Stasis can also work well to slow them down a little too.
Provided you can beat the hounds, you'll gain the Warrior's Fury Amber, and you'll also be able to loot the pig corpse nearby for some blood. However, we would also suggest checking the little shack nearby, as you'll find a bottle of Wine that could be a suitable alternative.
Should You Give Sheamus Blood Or Wine?

Return to Sheamus, and you'll be left with a choice to make. Do you give this madman some actual blood to disprove his mad demonic theory, or do you give him wine to feed into his madness?
Well, if you want maximum rewards, there is one clear answer. Here is what you get for each choice:
- Give Blood: 1x Ferrofluid Power Material + 1,000 Catalsysts
- Give Wine: 1x Ferrofluid Power Material + 3,000 Catalsysts
We would suggest giving him wine, convincing him of his immortal status, and deluding the poor boy into thinking he is a creature of the night.