One of the best strats is to start off with Obyn and your free dart monkey. You then save up for a ninja monkey in Obyn's range for nature's clarity buff. You then get that ninja to a 1-0-1 or 2-0-0 then get 2-0-1 from wherever you started from. Next upgrade that ninja to a 3-0-1. Buy another ninja in Obyn's range if possible and get it to 3-0-1. Get one of those ninjas to 4-0-1 then buff it with a 3-0-0 alchemist. Next get your other ninja to 4-0-1. After that get your two ninjas in a jungle drums village. After that, the rest of your money is basically up to you. Congrats! You've sped-run BTD6 on easy mode.