Category 5 Elusive Krasis

Amorphic. The Krasis is able to change shape in order to fit through spaces 1 inch thick at smallest. The Krasis always changes shape to fit into its surroundings. There are 3 specific amorphic forms available to the Krasis that affect its AC and max HP. All HP loss is carried over from the previous amorphic shape, even if this would result in the death of a Krasis. 

TINY (mouse-sized) - Max HP: 30, AC: 18. When tiny, the Krasis deals quarter damage.

MEDIUM (humanoid) - Max HP: 100, AC: 17. When medium, the Krasis deals half damage.

GARGANTUAN (base size) - Max HP: 300, AC: 15.

Biocamouflage. The Krasis can change its skin colour and body shape without restriction, provided it is either tiny, medium or gargantuan sized.

Assassin. The Krasis automatically passes stealth checks if underwater or in dimly lit/dark areas. If the Krasis makes an attack roll against a creature unaware of its presence, the Krasis automatically scores a critical hit and adds 40 (20d4) piercing damage to the attack roll.

Regenerative. At the start of each of its turns, the Krasis regains 10% of the max HP of its current amorphic form. Additionally, once a Krasis has been reduced to 0 HP, if any body parts are left intact the Krasis can regenerate fully from the body part over 24 hours.

Siege Monster. The Krasis deals triple damage to constructs.

Attack. The Krasis makes a single attack with its bite.

Bite. Melee Weapon Attack: +16 to hit, reach 5 ft., 1 target. Hit: 50 (10d8 + 10) [damage type] damage. If a creature dies as a result of this, it makes no sound whilst dying.