Parasite

Parasitic organisms that take over the host and use them as part of a hive collective objective to consume all life.

The parasite is a dark grey color.

Small tentacle appendages around what seems to be the parasite's mouth.

10 micrometers for basic parasite
15 micrometers for a queen

Depends on the creature it infects. The parasite turns the hosts body into a living weapon, turning limbs into bones spikes, growing extra body parts, absorbing more than one creature to one parasite host, etc. It's overall very gruesome. The parasite itself is a minuscule semi-flat worm with spider-like legs.

Strength in numbers
Biologically immortal
Able to infect mostly every living species

Extremely aggressive to everything living.

Will burrow into the hosts neck to infect.

Can create a small cocoon around itself.

Extremely small
Demonic magic

If there's enough on the ground: slimey hissing sounds

Anywhere. They can survive in any weather conditions.

Sacks containing fully grown parasites are laid by the host of the queen parasite.

Any biomass

Death
Famine