The Mimic - OSRS Wiki

The Mimic is a sporadic boss who can be fought by presenting a mimic casket to the strange casket found upstairs in Watson's house. Mimics can be obtained from an elite or master reward casket after asking the strange casket to enable the chance to obtain a mimic casket (which is disabled by default). The elite reward casket has a 1/35 chance of being a mimic, while master reward caskets have a 1/15 chance.[1]

Evil creature, Old School RuneScape Wiki

Keyhole (The Mimic) - OSRS Wiki

How I kill the Mimic Boss

The Mimic adds a little extra reward for you : r/2007scape

Treasure Hunter, The Mimic Rises, RuneScape Wiki

Keyhole (The Mimic) - OSRS Wiki

Accepted Suggestion - Game] Mimic aka clue scroll boss - Handled Suggestions - Alora RSPS

Mohg's Great Rune

TzTok-Jad - OSRS Wiki

Great Olm - OSRS Wiki

Accepted Suggestion - Game] Mimic aka clue scroll boss - Handled Suggestions - Alora RSPS

How to turn Mimic Boss On in OSRS / Where to find the Strange Casket