I'm not sure it's obvious from the terse descriptions below, but I've tried to craft each set of otherworldly beings (Demons, Devils, Great Old Ones, Archfey) with a different "theme." Demons are all about inspiring destructive and chaotic impulses that undermine civilization, Devils seduce mortals into seeking personal power, Great Old Ones inspire their agents to unravel cosmic mysteries and seek unknowable truths, and Archfey embolden the connection between mortals and the natural world.
Demons
Aleyus
– The Butcher
- Inspires mortals to wantonly shed the blood of their fellow men
- Portrayed as a hulking beast with a horned, animalistic head
Beldamus
– The Bringer of Madness
- Inspires mortals to drive others into the arms of insanity and nihilism
- Portrayed as a many-headed monstrosity that screams and whispers from its many mouths
Ozoga
– The One Who Slithers
- Inspires mortals to spread illness and disease to the innocent
- Portrayed as a monstrous snake or worm whose mouth is lined with venom-dripping fangs
Pyoric
– The Child of Flesh
- Inspires mortals to commit carnal excesses and breed demoniac progeny
- Portrayed as a slavering, wanton beast of ambiguous gender
Yanakus
– The Father of Undeath
- Inspires mortals to reanimate the dead as creatures of darkness
- Portrayed as a grave-bloated and pale man with the head of a rotten goat
Devils
Abzula
– The Sweet Seducer
- Inspires mortals to use lustful means to gain power and influence over others
- Portrayed as a beautiful woman clad in the furs and diadem of a wealthy noblewoman
Agrazus
– The Iron Hand
- Inspires mortals to take power by martial means and force of arms
- Portrayed as a soldier wreathed in flames and holding an impossibly-heavy hammer
Damazu
– First Among Hell
- Inspires mortals to bend others to their will through guile, stratagem, and intricate scheming
- Portrayed as an imperious man with cloven hooves who holds a bloodied scepter
Malistrad – The Infernal Sage
- Inspires mortals to seek knowledge hidden by the Church
- Portrayed as an old man bound by stout iron chains to a ponderous book of lore
Menoch
– The Apostate Minstrel
- Inspires mortals to use religion to enrich or empower themselves at the expense of others
- Portrayed as a young man or woman holding an ornate musical instrument
Great
Old Ones
The
Envoy of the Black Stars
- Associated with planar communion and otherworldly contact
- Portrayed as a luminescent, fungal abomination
The
Maiden of Dust
- Associated with prophecy and despair
- Portrayed as a ravening maw
The
Bloodletting Beast
- Associated with nightmares, doom, and unnatural births
- Portrayed as an empty shroud laden with chains
The
Pallid Emergence
- Associated with dreams and the moon
- Portrayed as an impossible thin and pale figure with writhing hair
The
Elder Scholar
- Associated with forbidden knowledge
- Portrayed as a mass of unblinking eyes
The
Inchoate Presence
- Associated with mystery, chaos, and unfathomable plans
- Never Portrayed directly
The
Hunger of the Void
- Associated with senseless violence and ceaseless propagation
- Portrayed as a monstrous, spider-like thing
Archfey
The
Foolish Maiden
- Emboldens mortals to abandon themselves in dreams and reverie
- Portrayed as a laughing woman crowned with wildflowers
The
Lover of Midnight
- Emboldens mortals to seek dark pleasures in the deep woods
- Portrayed as a cruel woman clad in cobweb and frost
The
Mountain Lord
- Emboldens mortals to join the Wild Hunt against those who have offended the fey
- Portrayed as an arboreal man with antlers wearing furs
The
Tempest Princeling
- Emboldens mortals to give in to their destructive and impetuous impulses
- Portrayed as an angry young man wearing a raiment of dark clouds
The
Verdant Knight
- Emboldens mortals to make war against civilization
- Portrayed as a towering knight clad in green armor and bearing a greataxe
The
Wild Queen
- Emboldens mortals to protect the natural world
- Portrayed as a shining woman gowned in waves of spring water and fallen leaves
Nicely formatted pdf of these here.