Okay, I know this is an art blog, but this has been festering in my brain for a while and I need to yap about it
Modri Vladis is a naturally occurring UNDEAD
I believe he's not a Bizarre Doll or a delusional human, but rather something in between.
Why naturally occurring undead?
Simple really. Strigoi, a Romanian folklore precursor to the modern vampire; and Vlad Dracul (Romanian for "dragon"), better known as Vlad the Impaler and historical inspiration behind the iconic Count Dracula.
Also because I'm slavic and read the poem Svatební Košile (rough translation: Wedding Shirt) from the collection of ballads Kytice (Bouquet) by Karel Jaromír Erben. Quick summary of the poem: a grieving girl is praying to the Virgin Mary, but it's more like blasphemy (she begs for her own life to be cut short as she has nothing else to live for), her significant other returns, not alive, but as a living dead, shenanigans ensue and in the morning she's traumatised for life and repents for her sin.
How does this fit in to my unhinged theory?
Bizarre Dolls are artificial as we saw in Book of Atlantic/Luxury Liner Arc. However, I don't think Modri fits the mold of how a Bizarre Doll behaves. He seems far more advanced that R!Ciel and I highly doubt UT would waste resources just to fuck around with Sebastian.
If we assume for a moment that in the world of Kuroshitsuji/Black Butler more supernatural beings in addition to Demons and Grim Reapers exist, we can assume that a vampire, a gothic staple, is pretty fitting for the setting and although stereotypically a Romanian fair, it's not that hard to cross Europe and cross the La Manche channel to England.
If UT met Modri somewhere, it wouldn't have been hard for UT to study a natural undead and refine the Bizarre Dolls. Then the trip to France UT underwent in Emerald Witch Arc might have been to get Modri to England.
I did say delusional, here's why:
If Modri Vladis is indeed a natural undead (a Vampire), his memories may have been tampered with to make him believe Sebastian is the one who did this to him. A Grim Reaper with a death scythe could be capable of memory manipulation like this once they figure out how to splice fake records with real ones.
Who did this to Modri originally?
Could be a vampire sharing the "gift" of immortality (a part of the "Hell" Modri mentioned). Or could be another demon's fuck up. Could be either, but seeing as Modri is religious his use of "demon" might be more loose than we are lead to believe.
Modri's "Hell" is thirst for human blood
Why? Because we see him with a stylised blood infusion stand. This could be the only way to keep Modri from killing people. He needs blood to survive, so a method of ingestion that doesn't stir his taste buds might be necessary since it appears he may have never been taught to control himself when feeding.
Tl;Dr: Modri got turned into a vampire against his will, got his memory tampered with and now believes Sebastian did it to him.