Seems like you didn't receive my PM, so i sent you an email on tour Gmail account, please let me know if now everything Is ok!
Yeah, the mimic Is one of the secret superbosses, level 6 Is absolutely too low, i suggest you to finish the game before, since secret quests should be started at lv 8.
One special note for the Misty area: never ever save in the save point behind the spectral haze if you don't have enough Blood vials to defeat another spectral haze and so escape from Misty area 4... Spectral haze Is the strongest normal monster of the game and will probably make you waste at least one Blood vial if you are below level 9.
On a side note Mimic Is designed for a player at level 9 or you'll get mincemeated in case you stumble in its deadly Attack.
There are some monsters which provides healings with higher drop rates anyway