A blatant rip-off of Return of the Living Dead zombies:

Alchemical Zombie is a template that can be added to any humanoid or monstrous humanoid. They are created by a highly infectious gaseous chemical.

Size and type: changes to undead. Do not recalculate base attack bonus, saves, skill points. Size is unchanged.

Speed: Same as base creature.

Armor Class: The creature's natural armor increases by 2.

Attack: The creature gains a bite attack dealing 1d4+STR and two claw attacks dealing 1d4+STR

Special Attacks: None.

Special Qualities:

An alchemical zombie has an inescapeable craving for brains, using the electrical impulses from neurons to dull the constant pain of rotting. They prefer the brains of intelligent creatures, as animal brains only give them mere minutes of relief. A fresh alchemical zombie must feed on the brains of intelligent creatures every 8 hours. A moderately decomposed alchemical zombie must feed every 4 hours. A badly decomposed alchemical zombie must feed every hour. If deprived of brains for too long, it becomes ravenous and attacks the first intelligent creature it comes across.

An alchemical zombie gains the scent ability.

Disease-Living Death-bite or claw-FORT DC: 15+HD. Incubation: 1 hour. Damage/Secondary: 1d6 CON, 1d6 STR, 1d6 DEX. Those who die of Living Death rise as an alchemical zombie 1d4 rounds later.

Split: If an alchemical zombie takes damage equal to half its maximum hit points from a single slashing attack,it instead splits with all pieces remaining animate. Roll 1d4. On a roll of 1-2, a hand is detached. On a roll of 3, the head is detached. On a roll of 4, the torso is split along the middle. The severed parts and main body have HP equal to half the whole body's hit points. Severed hands have a move speed of 30 and retain their claw attack. Severed heads are immobile and retain their bite attack. A split upper body has a move speed of 10 and retains its attacks. A split lower body retains its move speed but has no attacks. Severed body parts can be re-attached with a DC:20 Heal Check.

Invulnerability: If reduced to 0 HP, an alchemical zombie is not destroyed and remains animate and mobile unless its body has been completely annihilated. This can be done with a disintegrate spell, dissolving in acid, complete cremation (this is a bad idea*). If an alchemical zombie is reduced to 0 HP by cold damage, it becomes dormant for 1d4 hours. If an alchemical zombie is reduced to 0 HP by electricity damage, it is destroyed as normal.

If an alchemical zombie is destroyed by fire damage, the chemical animating is released and can infect the living in a 30 ft radius with the living death disease if they breathe it in. If it escapes into the sky, it rises into the sky and infects a cloud. This causes the chemical to rain down in a diluted form, harmless to the living except causing odd tingling. Any corpses within a one mile area exposed to the contaminated rain (including those buried) rise as an alchemical zombies 2d4 minutes later.