Its blood/internal organs produce and are sustained by a highly corrosive substance. Upon the creatures death all those surrounding it must make a dc15 dex saving throw  or take 2d8 acid damage.

All (non-magical or silvered)weapon attacks that do piercing/slashing damage and succesfully hit the creature give the weapon a -1 to its attack and damage rolls, reaching -5 destroys the weapon (rust monster rules yo).

Abberant parasite (young) make either 2 claw attacks or 1 bite attack.

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., 1 target. Hit: 4 (1d4 + 2) piercing damage. 
On being hit target must make a dc12 Con Saving throw, if not take 2d6 poison damage and become poisoned until the end of their next turn.

Claws. Melee Weapon Attack: +4 to hit, reach 5 ft., 1 target. Hit: 5 (1d6 + 2) piercing damage. 

Skitter. After succesfully attacking, the parasite can move up to 15ft away from the target while imposing disadvantage on an opportunity attack from the target it attacked. If it has broken line of sight, or is otherwise obscured from the target it can perform the hide action.

Pure Savagery.

If another abberant parasite succesfully performs a bite attack and this one is within 5ft of the same target it may perform a single claw attack.