On the level "Road to the Castle," when you run into the green lerpcaugn, you must protect his pot of gold without it taking damage just kinda like the grump old man achievement except this one is a lot harder. This one is almost impossible for you to get unless you have at least 3 people helping you. What you need to do is have a friend working the tank, you on a turrent and another friend planting turrets and radios to keep those monsters off of that pot. If you do this right you should get it. Remeber that the pot canno't take ANY damage at all.