The first grandfather mimic doesn't recall the exact moment it realized time is truly just as malleable as its form. This is mostly because at that point time ceased to be for the monstrosity. Its primative mind expanded and it learned how to play with time to suit its ends. Some think this drove the mimic mad. In fact, all its descendants are quite chaotic. Some strive to make the world around them better, others to sate their own hungers, and the last to tear it all down. They are all well-armed for this with the ability to at least temporarily age foes and even step out of time for a few ticks. At least one works out of a detective's house, aiding the investigator hiddenly when they can't piece a puzzle together.

Grandfather Mimic

Medium Monstrosity (shapechanger), often chaotic

Armor Class 12 (natural armor)

Hit Points 127 (17d8 + 51)

Speed 15 ft

Str 16 Dex 13 Con 16 Int 14 Wis 16 Cha 8

Skills Arcana +5, Investigation +5, Stealth +7

Damage Immunities acid

Condition Immunities prone

Sensesdarkvision 60 ft, passive Perception 13

Languages understands Common, Draconic, and Elvish but cannot speak

Challenge 6 (2,300 XP)

Shapechanger.

The mimic can use its action to polymorph into a grandfather clock or back into its true, amorphous form. Its statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.

Adhesive (Object Form Only).

The mimic adheres to anything that touches it. A Huge or smaller creature adhered to the mimic is also grappled by it (escape DC 13). Ability checks made to escape this grapple have disadvantage.

False Appearance (Object Form Only).

While the mimic remains motionless, it is indistinguishable from an ordinary grandfather clock.

Grappler.

The mimic has advantage on attack rolls against any creature grappled by it.

So Fluffy (Object Form Only).

Whenever a creature is grappled by the mimic at the start of their turn, they must succeed on a DC 12 Charisma save or be Charmed until the end of their turn. If the mimic dealt damage to the creature last turn, the creature has Advantage on this save.

Actions

Multiattack. The mimic makes two pseudopod attacks.

Pseudopod.

Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 8 (1d10 + 3) bludgeoning damage. If the mimic is in object form, the target is subjected to its Adhesive trait.

Bite.

Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 8 (1d10 + 3) piercing damage plus 9 (2d8) acid damage.

Mimic Time (Recharge 5-6).

The mimic chooses a creature it can see within 60 ft. and temporarily accelerates its aging. The target must succeed on a DC 14 Wisdom saving throw or be affected by the Slow spell for 1 minute. If the save fails by 5 or more, the target also ages 1d4 x 10 years. If a target's saving throw is successful or the effect ends for it, the target is immune to this mimic's Mimic Time action for the next 24 hours. The aging effect can be reversed with a greater restoration spell.

Between Moments (1/long rest).

The mimic briefly stops the flow of time for everyone but itself. No time passes for other creatures, while it takes 3 turns in a row, during which it can use actions and move as normal.

This action ends if one of the actions the mimic uses during this period, or any effects that it creates during this period, affects a creature other than the mimic or an object being worn or carried by someone other than the mimic- unless either is grappled by the mimic. In addition, the spell ends if the mimic moves to a place more than 1,000 feet from the location where it used this magical ability.