Ability Score. Str, Con and Wis scores each increase by 1.
Monstrosity. Your creature type is monstrosity.
Age. Mimics reach what passes for adulthood at around 10, but can live as long as a century.
Size A mimic's true form is amorphous, but can draw itself up to a height of about 6 feet. Your size is Medium.
Speed. Your base walking speed is 15 feet.
Shapechanger. Your natural form is amorphous and as an action you can polymorph into an inanimate object of Medium or Small size that you have seen, or back into your true form. You retain all of your normal statistics while in this form.
Any equipment you carry can be contained within you (as long as your shape has the dimensions to accommodate it), dropped or used if appropriate. If you die, you revert to your true blob form.
Unassuming Form. While polymorphed as an unassuming object you are considered hidden (full cover). As long you do not move you are not spotted by perception checks and other creatures have disadvantage to investigation checks to detect that you are not a normal object.
Suprise Attack. If a Large or smaller creature enters a space within 5 feet of you (or simply interacts with you), you can use your reaction to rapidly extend up to two of your limbs and make an attack against the creature. If you attack you are no longer considered hidden.
Amorphous Grappler. You are able to form pseudopods that give advantage on grapple checks
No Armor. Due to the amorphous nature of your true form, you cannot benefit from armor, though you can use a shield. Your natural Armor Class is equal to 12 + your Dex modifier and you are immune to the prone condition.
Starting at 5th Level, you can form a hardened carapace on yourself (cast the barkskin spell without material components). You regain the ability to do so when you finish a long rest.
Bite. Your maw is a natural weapon, which you can use to make unarmed strikes. If you hit with it, you deal piercing damage equal to 1d4 + your Str, At 6th level, your bite deals an additional 1d4 acid damage.