Mimic ---> Mumic
An undead mimic which poses as a sarcophagus. The mummy inside is covered in gems to be a false target and lure potential victims closer. The exact process for creating a Mumic is shrouded in mystery. Of the few encountered, some seem to have a connection to Arcane magic and some seem to be more Divine in nature.
If Arcane: Rumors suggest that, if the Mumic eats a spell caster, it has a 1 in 6 chance to learn how to cast a spell known to that caster. The typical Arcane Mumic knows 2 cantrips: Chill Touch, and one other cantrip chosen from any arcane class's spell list. An Arcane Mumic has the ability to cast Chill Touch as a bonus action three times per encounter. Additionally, an Arcane Mumic typically knows 1d8 1st-Level-Spells (which can be from any arcane class's list); it can cast each of those spells once during an encounter. An Arcane Mumic uses its choice of either CON or INT to determine spell attack bonus and save DCs. Necromancy spells are the most common known, but an Arcane Mumic is not limited to necromancy.
If Divine: The Mumic was created to serve as a guardian for [insert thing or person here]'s burial treasure. A Divine Mumic has knows 4 1st-Level-Spells chosen from either the Cleric or Paladin spell list; a Divine Mumic also has 4 1st-Level-Spell slots. It can use it's spell slots either to cast spells or to Smite -similar to a Paladin of 3rd Level, but the damage can be either necrotic or radiant. Additionally, a Divine Mimic has two uses of Channel Divinity: Path to The Grave (as a Grave Domain Cleric) and Champion Challenge (as an Oath of the Crown Paladin). A Divine Mumic uses either CON or WIS to determine spell attack bonus and save DCs. Typical spells known by a Divine Mumic are Command, Inflict Wounds, Bane, and Wrathful Smite (but others are possible).
More Advanced Mumics: Higher spell slots are possible (but will increase bookkeeping for the DM). Other options may include having the body inside the Mumic be an animated skeleton which joins the fight. Lair actions may be appropriate depending on the encounter.
