Planar Bestiary
This singular entity, an ancient primordial of icy undeath, was imprisoned. But some whisper that Winter (as their name is often shortened to) is free of the Primordial Chaos. Or maybe they're just an avatar that's loose, walking the planes, "blessing" undead. For what reason isn't known, but some guess it is to gather a force to oppose Qoreth-shemkur.
Motive: Mysterious, oppose Qoreth-shemkur
Environment: The Elemental Chaos, the Shadowfell, cold regions of the Material Plane, alone or attended by undead, icy elemental creatures, and potentially one Winter herald
Health: 90
Damage Inflicted: Major wound (11 points)
Armor: 5
Movement: Short; long when flying
Modifications: Speed defense as level 6 due to colossal size; history, magic lore, and necromancy lore as level 10
Combat: Winter attacks twice each round with their winter blade (which can reach a short distance), inflicting damage, and on a failed Might defense task, an additional 6 points of Speed damage (ignores Armor) from either cold or necrotic energy, whichever is most effective against the target.
Winter can exhale a blast of cold and necrotic energy every few rounds, filling an adjacent area a short distance in diameter. Creatures in the area that fail a Speed defense task suffer 9 points of Speed damage (ignores Armor) and are encrusted in ice, preventing them from moving from that spot and hindering all their physical tasks until they break free with a successful Might-based task as their action. Encrusted victims also take 3 points of Speed damage (ignores Armor) each round from necrotic energy pulsing through the ice.
Winter can use magic to detonate explosions of cold within very long range, create impressive walls of ice within long range, dispel other creatures' magic, and create undead (up to a level 5 creature). Once per day they can magically call down massive meteors of ice in an area a long distance in diameter that inflicts damage on all creatures and structures in the area, or attempt to immediately kill a living target of their choosing within long range.
All tasks (including attacks and defenses) of undead within short range of Winter are eased. While at least one undead is within short range of Winter, Winter regains 5 points of health per round.
Winter is immune to cold, electricity, necrotic, and poison attacks, but is vulnerable to fire; every time they take fire damage, they take 5 additional points of damage.
Interaction: The Tomb of Winter speaks in the language of elder elementals (Primordial) and telepathically. They rarely deign to notice the living unless it is to question them about recent sightings of Qoreth.shemkur or cultist activity of the same. Undead are inclined to trust Winter, even intelligent ones. Winter may bargain with other creatures that agree to accept an undead created by Winter into their group. Such an undead proves to be more of an observer than an ally, however.
Use: A necromancer gathers materials and lore to perform a powerful ritual, one meant to free an ancient primordial from eons of imprisonment. Undead attack a nearby structure, supposedly a shrine to some local deity. It's actually home to a cult of Qoreth-shemkur; many innocents are caught in the middle.
Loot: Winter's "winter blade" shrinks down to greatsword-size (heavy weapon) if Winter is destroyed or if they give the weapon away to an undead wielder. In another creature's hands, the sword is an artifact that inflicts an additional minor wound (3 points) (ignores Armor) with ice or cold, whichever is most effective against the target (level 9; depletion: 1–3 in 1d100; if depleted, Winter is summoned to their blade, or Winter is reconstituted if they were previously destroyed).
GM Intrusion:
When the Tomb of Winter takes damage, a blizzard of icy crystals immediately howls from the wound back toward the attacking character within long range. The attacker and any other creature between them are subject to the effects of Winter's breath of cold and necrotic energy (see Combat), even though it's not Winter's turn.
GM Intrusion: Winter attacks with their blade or casts a spell immediately, even though it's not Winter's turn.