Demon availability by progression

Data collected using version 1.03 Steam on Nightmare NG+.

Game Start

 * Dullhammer
 * Morte
 * Aello
 * Seama
 * Cannon Morte
 * Bat
 * Bone Morte
 * Ghost
 * Giant Rat
 * Dullahammer Head
 * Vepar
 * Forneus
 * Blood Grinder Knight
 * Sabnock
 * Giermund
 * Moco Wood
 * Barbatos
 * Plume Parma
 * Toad
 * Gargoyle
 * Zangetsu (first fight)
 * Killer Barber
 * Buer
 * Demon
 * Poltergeist
 * Cyhyraeth
 * Ordog
 * Nyabon
 * Bloodbringer
 * Craftwork

After Craftwork

 * Caraboose
 * Simian
 * Decarabria
 * Shovel Armor
 * Chair Mimic
 * Buer Armor
 * Malediction
 * Zagan
 * Lili
 * Carriage Morte
 * Puppy
 * Wolfman
 * Shield Outsider
 * Celaeno
 * Leraje
 * Thunder Elemental
 * Gusion
 * Rul'sha
 * Dantalion
 * Andrealphus

After Double-Jump

 * Axe Outsider
 * Ocypete
 * Light Elemental
 * Gamigin
 * Bloodless
 * Titania
 * Tamako-Death
 * Dragon
 * Mimic
 * Triwheel Buer
 * Abyssal Guardian
 * Archdemon
 * Eight-Bit Skull
 * Eight-Bit Bat
 * Eight-Bit Zombie
 * Eight-Bit Overlord
 * Poison Toad
 * Twin Dragons

Here the path splits, depending whether you got the Blood Steal shard or the Silver Bromide