Enemies in Amalgam

Take a bunch of little monsters. Put them in a pile. Add a drop or two of mercury. Squeeze. Congratulations! You just manufactured an Amalgam.

Mechanically, Amalgams are a ruling for any kind of modular enemy. Take twelve HD¼
critters and fuse them into a HD 3 creature with extra powers. Every time the big creature takes damage equal to (or greater than) half the health of a little one, said little one blows off the big critter.

Amalgam Examples

Poes - HD¼

Can phase through walls. Attack with spectral claws and cold fires. Can't amalgamate in the presence of torchlight. Killed by sunlight.
HD ≤ 1: Can only be hit by magic and magic weapons. Afraid of fire.
HD ≥ 2: Gains coldfire blast attack.
HD ≥ 4: Sheathes self in ancient silks and armour.
HD ≥ 6: Wears bronze crown. Can spew forth 3d4 little poes 1/week.

Slimes - HD½

C'mon you know this one.
HD ≤ 1: Thin enough to melt through your skin into your blood. Attracted to, and killed by, fire and salt.
HD ≥ 2: Can melt skin.
HD ≥ 3: Psuedopod attack. Can melt wood.
HD ≥ 4: Swallow attack. Can melt steel. ¼

Cronenbergs - HD1
Each has a weaponisable mutation. The horrible result of their fusion will carry all their best traits. This one has a:

1. Heaving brainsack. Its veins throb in magnetic rhythms, grant mild telekinesis
2. Suckered mouth tentacle. Can latch onto almost any surface. Strength check and a knife to get it off your neck
3. Feather-tipped biowhip. Hurls sharp quills in 3d4 damage burst, each d4 to a chosen target. 
4. Reverberation chamber. Can spend the round hooting to deal 1d6 damage to everything within 50 feet
5. Birthing sack. Thrown a short distance it bursts to reveal another Cronenburg with only 1hp
6. Chitin and fat crumple zones. Double health for individual Cronenburg.
7. Fibrous asbestos mane. Resists fire, releases toxic clouds when damaged. Save vs coughing fit
8. Abdominal maw. Womb holds surprising amount, mutates contents
9. Antenna array. Communicates with the hindbrain using odd gesticulations
10. External nervous system. Continuous contact will shut down muscles, bare nerve endings eventually assuming control
11. Biolumenscent blood. Eyes glow like torches. Can flash to blind all those looking 1/day
12. Spinal whips. Two extra spinal columns sprout from back like cobras. Each attacks independently, lashing for 1d4
13. Impact claw. Shockwave from claw snap blows away all in front of it. Takes a turn to rearm
14. Caustic sinuses. Exposed orifices puke sticky, rancid mucus. Burns for 1d4/round until scraped off