Hit Dice: 7d12 (45hp)
Initiative: +7 (+3 Dex, +4 Improved Initiative)
Speed: 40ft.
AC: 17 (+3 Dex, +4 natural), touch 13, flat-footed 14
Attacks: 2 Claws +6 (+3 Base, +3 Dex)
Damage: Claw 1d4+2 and 1d3 cold
Face/Reach: 5 ft. by 5 ft./5 ft.
Special Attacks: Dex damage (Su)
Special Qualities: Create Frostskull, Darkvision 60', light sensitivity, Spell-like abilities
Saves: Fort +2, Ref +5, Will +5
Abilities: Str 14, Dex 17, Con -, Int 13, Wis 10, Cha 15
Skills: +8 Balance, +6 Concentration, +12 Listen, +13 Hide, +13 Move Silently, + 12 Spot,
Feats: Alertness, Improved Initiative, Weapon Finesse

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Climate/Terrain: any cold or underground
Organization: Solitary, pair, or clutch (3-10)
Challenge Rating: 5
Treasure: 1/2 standard
Alignment: always neutral evil
Advancement: By character class, favored class Rogue

A Frostskull is a variety of undead that originates in cold climates. They are distigueshed by thier black flesh, and the electric blue glow on their claws, ribs, and on the bony ridges of their face (in the shape of an "evil skull"). Most Frostskulls dwell in caves or underground.
Their favored tactic is to use their Silent Image ability to create an illusionary Frostskull to distract their victim, while the Frostskull flanks their prey. It is not unheard of for older Frostskulls to gain class levels, typically in Rouge, though any class is possible.

Create Frostskull (Su): A humanoid or monstrous humanoid slain by a frostskulls energy drain attack rises as a frostskull 1d4 days after death.
[Note, Frostskulls created out of larger, or smaller humanoids would spawn as a Frostskull of the appropriate size so the stats and CR would have to be adjusted to compensate]
Dex Damage (Su): If a frostskull hits a single creature with both claw attacks in a single round of combat, the creature must make a Fort. save (DC 15) or it takes 1d6 temporary Dex damage, and the Frostskull heals that many hit points.
[A quick note, the Dex drain represents the chilling effect the Frostskull's attacks have on its victems]
Light Sensitivity (Ex): frostskull suffer a -1 penalty to attack rolls in bright sunlight or within the radius of a daylight spell.
Spell-like abilities: (as 7th level sorcerer) 3/day Silent Image