You can use the thief line classes to steal common items from enemies via stunning them in the open world, normally this isn't worthwhile but against mimics specifically it is incredibly powerful as their common drop is a AEXP item.
You can do this with any mimic provided that you are low enough level to still fight them in the open world and don't kill them. (you can reset their health by leaving the area and coming back most often via using the cat to go to akademia and back.)
Here in the Disgraced Ruins theres a room with 2 high level mimics that drop the 3000 aexp item when stunned.
(you can also use them to farm up water for purifying via stealing and running away.)
This takes basically no resources or specific strategies and you can always just swap to a gunner line and stun them through the door to heal.
Best of all this area specifically lets you make a mistake and accidentally kill the mimics and they will respawn.