Requirements
- either MWSE / OpenMW(0.49)!

Load order
1. Devilish Vampire Overhaul.esp (can be used on its own without TR Mainland, OAAB or Tamriel Data!)
2. ( TR_Mainland.esm )
3. ( Devilish_Vampire_Overhaul_TR_Dialogue_Patch ) -> If you use Tamriel Rebuilt, please also install the dialogue patch.

Installation:
-OpenMW users must activate Devilish Vampire Overhaul.esp + Devilish Vampire Overhaul.omwscripts
-MWSE users must activate Devilish Vampire Overhaul.esp and use the MWSE updater after installing this mod

How this mod works (Important!)

MWSE:
-MWSE users can only feed from NPCs.
-MWSE users must crouch / sneak and "activate" on the dead victim to feed.

OpenMW:
-OpenMW users must only crouch / sneak to feed from their victim.
-OpenMW users can feed on certain creatures as well such as rats.

Both:
- can fill up to three flasks of blood for transportation
- must use closed helmets to hide their vampirism or they'll be attacked
- cannot drink blood while wearing a closed helmet (duh).

ID List of UNENCHANTED helmets that work to conceil vampirism:
cephalopod_helm
bonemold_helm
fiend helm
netch_leather_boiled_helm
chitin helm
chitin_mask_helm
morag_tong_helm
chitin_watchman_helm
dust_adept_helm
mole_crab_helm
indoril helmet
orcish_helm
bonemold_armun-an_helm
bonemold_chuzei_helm
bonemold_gah-julan_helm
redoran_master_helm
dwemer_helm
ebony_closed_helm
iron_helmet
steel_helm
daedric_god_helm
daedric_fountain_helm
daedric_terrifying_helm
nordic_iron_helm
daedric_helm_clavicusvile
... (to be expanded)

(There's currently no option for beast races but you can use my other mod "Of Melodies and Moonlight" and use the painter's hat (id: AB_a_NetchimanCap ) to hide your vampirism, which works for beast races as well).

Closed OAAB helmets are added via my "Of Melodies and Moonlight - A Sadrith Mora Artist" mod which requires OAAB and TR Data anyway and already utlizises a tiny snippet of this mod's script to hide vampirism via helmets. Of Melodies and Moonlight can communicate with this mod via the global. Therefore, it is able to extend this mod. 

Option 1: Vampires get stronger:

Blood Thirst
Stage 1: Fortify Strength + Fortify Speed (+05), Drain Agility & Personality (-05) ( Plus sun damage )
Stage 2: Fortify Strength + Fortify Speed (+10), Drain Agility & Personality (-10) ( Plus sun damage )
Stage 3:Fortify Strength + Fortify Speed (+15), Drain Agility & Personality (-15)) ( Plus sun damage )
Stage 4:Fortify Strength + Fortify Speed (+20), Drain Agility & Personality (-20) ( Plus sun damage )
Stage 5: Fortify Strength + Fortify Speed (+25), Drain Agility & Personality (-25) ( Plus sun damage )
Stage 6: Fortify Strength + Fortify Speed (+30), Drain Agility & Personality (-30) ( Plus sun damage )
Stage 7: Fortify Strength + Fortify Speed (+35), Drain Agility & Personality (-35) ( Plus sun damage )
Stage 8: Fortify Strength + Fortify Speed (+40), Drain Agility & Personality (-40) ( Plus sun damage )

Option 2: Vampires get weaker:

Blood Thirst
Stage 1: Drain Strength + Drain Speed + Drain Agility + Drain Personality (+05) (Plus sun damage )
Stage 2: Drain Strength + Drain Speed + Drain Agility + Drain Personality (+10) (Plus sun damage )
Stage 3: Drain Strength + Drain Speed + Drain Agility + Drain Personality (+15) (Plus sun damage )
Stage 4: Drain Strength + Drain Speed + Drain Agility + Drain Personality (+20) (Plus sun damage )
Stage 5: Drain Strength + Drain Speed + Drain Agility + Drain Personality (+25) (Plus sun damage )
Stage 6: Drain Strength + Drain Speed + Drain Agility + Drain Personality (+30) (Plus sun damage )
Stage 7: Drain Strength + Drain Speed + Drain Agility + Drain Personality (+35) (Plus sun damage )
Stage 8: Drain Strength + Drain Speed + Drain Agility + Drain Personality (+40) (Plus sun damage )

If you drink blood you'll be back at stage 0 (no effect). Everyday you don't drink blood you'll progress to the next stage.

Credits:
Sjek for his OpenMW lua script
Hrnchamd, Merlord and Greatness7 for their MWSE script.
Version 1.5 merges in Vampire Player Hit Sounds by i3ncore

But DetailDevil, I want to test your mod first before starting my playthrough. How do I do that?

1. Go to a safe that you don't care about for testing purposes or create a new one
2. Open the console with ^ and type player->addspell "Vampire Blood Quarra"
3. Rest for 3-4 days far away from a town until you turn into a vampire
4. Give yourself a closed helmet to hide your vampirism via: player->additem "cephalopod_helm" 1
5. Remember to unequip your helmet and to crouch / sneak  (+ activate) to drink blood from corpses.
6. Test whether you like my mod