1. You have three people in your party. level all your characters to lvl 3.
2. Warrior skill: stone war (left column), Heal wound (left column), Taunt
3. Archer skill: Fire arrow (right column), mark target, smoke screen, traps
4. Mage skill: Heal totem, summon ent (left column), earth fury, ice cloud
5. Strategy: always use warrior to taunt mimic, maintain a high hp to avoid death by mimic's combo
6. Kite mimic around the low fence, let your warrior lure the mimic, but don't fight if possible
7. If mimic pulls your archer or mage, you have two way to save them, circle a low wall around mimic or use warrior's party heal
8. stone wall can be casted often to trap mimic, make sure you still have the mana to heal yourself/party or taunt it
9. In stage two and three, mimic could release an AOE to daze you characters, you may cast an ent as a bait before it is released and teleport your archer as far away as possible, or you can just trap it within the stone wall.
10. Theoretically, you should be able to kill mimic even in epic diffiuclty with the above tactics.