So, recently i've helped Diothebanana get fire rage orb. I've gotten the orb solo before but it was easier than duo. I've put together a strategies that work pretty well for duo runs. This work better with orbs but it work fine without orbs.
Player 1: Rengoku 6* with bomba orb, black beard 6, dio, saleman/bulma with cost orb, erwin, 1 freeslot for a dps or whatever
Player 2: Meta knight with bomba orb, saleman with cost orb, dio.
Player 1 will be the only person defending while player 2 tries to farm as efficiently as they could.
You need to skip wave 1,2,3,4 but clear wave 5 and 6 to help with the pressure later on.
Details:
Player 2 place a farm as soon as possible, preferably before choosing phase between extreme and normal end.
Player 1 place a rengoku at the front of the first path where enemies spawn,put the priority to last, this rengoku will be call 1st rengoku . Player should be able to focus on farming until wave 4.
When the decelerate reach the base, by then player 1 should have an upgrade 2 saleman/bulma and should be able to place another rengoku (2nd rengoku) down when the enemy is about to reach the base. This rengoku will be set to first.
After the enemies close to base is take care of, upgrade your 1st rengoku to 2nd upgrade while farming. Stop skipping at this point and clear 2 waves. During those 2 waves, place another rengoku opposite to the 2nd rengoku, which will also be set to first. This is the 3rd rengoku that you will place.
Farm and upgrade the rengoku if necessary, especially the 1st rengoku.
When it's wave 7, keep skipping until wave 13. At wave 13, you should stop skip. player 2 should have a max farm and should be able to place down a meta knight, but not yet. Player 1 should have the 1st rengoku upgrade to max and 2nd and 3rd rengoku upgrade until it have the circle aoe. It is very important for player 1 to watch the boss hand and kill it as soon as possible by changing the priority if necessary. Immediately after the last boss hand die player 2 need to deploy meta knight and upgrade it if they have enough money, and use meta knight to help player 1 defend. Player 1 should deploy 2 max erwin to help buff meta knight, and then deploy another 2 max erwin to perform the cycle buff. The meta knight player should be able to kill the very tanky cloner with max erwin buff. This is one of the most important wave
Wave 14, player 1 need to spent all the money from wave 13 to place max out saleman/bulma. Player 2 need to focus on killing the boss hand first before moving on to others target. Keep skipping to wave 16.
Sell all of the tower unit at wave 16. Player 1 should use the money to place down 5 black beard at second upgrade spreaded out. Player 1 should also plac down 4 more erwins because the 4 erwins are sleeping. Player 2 should upgrade meta knight with all the money they have, then use the extra money to timestop and buy sometime. At this wave, winning should be easy as long as player 1 do not mess up the buff.
And there you have it, fire rage orb.