Can be one of the item asked for "San d'Oria's Stock and Awe II" Campaign Ops. I farmed Coopercap in North Gustaberg [S} on the hill. Killed about 50 with TH4 before i get an Agaricus. I might have been a little unlucky but i heard that it's for sure a hard drop to get. You can aslo get Coopercap mobs in Rollanberry Fields [S}. Good luck!
The fastest way to farm Agaricus is not on Thief. I have a Thief with TH9. Take forever to get a drop.
Instead, use the shotgun approach on BST with Warlike Patrick pet. Aby-LaThiene F-7 has a valley of 11 Cankercaps. Gather all the funguar with your lizard pet and use Fire Ball to kill them all. I have Chaack Belt (gives th1) equipped for the pet Ready command. You will get 1-7 Agaricus to drop each pull. About 7-8 stacks of Agaricus in 2 hours. The Cankercaps respawn about a minute after killing them.
Also lots of money drop chests for proc'ing Amber lights with your pet kills. Bring lots of Forbidden Keys!
Win-win! Good luck with those Marine Stewpot food.
I killed 422 Coppercaps last night in North Gustaberg [S].Thief with TH3
7/422 on the Agaricus.I have a +15 steal gear set,Quesyshroom was used 46 times and I stole each time and got 6 Woozyshrooms.Numbshroom is very rare, out of 422 kills it was used 2 times and got 1 Danceshroom stealing after it.If it really is possible to steal Agaricus from these, its less than 1%.