BioGoblin

Copy. The BioGoblin is able to copy all the abilities of another creature by eating its head. It can as well eat the ends or tips of weapons, which allows it to turn its hands into copies of whatever weapons it ingested. Lastly, the BioGoblin can eat solid matter to allow its body to take the same properties. (EX: the BioGoblin eats a mouthful of sand. It can now turn its own body into sand.)

Immortal. After dying by any means, the BioGoblin will come back to life after 12 hours have passed.

"Immortal". The BioGoblin possesses regenerative properties so efficient that it can practically save itself from death. When its hit points are reduced to 0 in a battle, it will be brought back to life with full hit points and continue the fight. To ensure that the BioGoblin stays down, the final blow must be specified to remove its head in any way.

Apex of the Fog. After spending a week in the Abyss, the BioGoblin has become the ruler of all that live within. 

 Punch. Melee Attack: +20 on hit, reach 6ft, one target. Hit: (10d10) bludgeoning damage. A creature hit with this attack must make a DC 18 Dexterity saving throw or be stunned for 1 turn and Prone. 

Stomp. Melee Weapon Attack: +14 on hit, reach 6ft, one target. Hit: (5d10) bludgeoning damage. The BioGoblin stomps on a creature as hard as it can. If the targeted creature is currently Prone, they will be Grappled until they make a Strength check of 17. They can as well be freed if the BioGoblin moves for whatever reason.

Bite. Melee Weapon Attack: +15 on hit, reach 3ft, one target. Hit: (1d10) slashing damage. If the BioGoblin kills a creature with this attack, it will eat their head and use its Copy ability. Bite can as well be used on inanimate objects to use Copy.

Dragon Breath (Recharges 1-2). The BioGoblin unleashes a terrible breath in a 60-foot cone. Each Creature in that area must make a DC 18 Dexterity saving throw, taking 31 (7d8) fire damage plus 49 (11d8) necrotic damage and they are afflicted with dragonblight for 1 minute on a failed save, or half as much damage and are not afflicted with dragonblight on a successful one. The afflicted target can repeat the saving throw on each of its turns, ending the effect on itself on a success.

Skewer. Melee Weapon Attack: reach 6ft, one target. Hit: (4d10) piercing damage. The BioGoblin's noise extends to resemble that of a swordfish's. He then uses this to skewer through Creatures.

Fog Clone. At the beginning of the BioGoblin's turn, it can create a clone of itself completely made out of fog that copies everything the original does. The fog clone disappears once the BioGoblin takes damage.

Fog-a-port. The BioGoblin can enter a cloud of fog to teleport to warp to a new location.

Sand-morph. The BioGoblin can turn its body into sand to avoid an attack, moving in any direction up to double its speed in the process. This can be done up to 6 times per battle.

Rapier-finger. The BioGoblin can negate the damage of an incoming melee attack by blocking with its finger extended into the blade of a rapier. In the same moment, the BioGoblin is able to use its rapier-finger to attack against the creature that initially attacked him while ignoring their AC, dealing (4d10+10) piercing damage. This can be done up to 6 times per battle.