Regrow (or Regen) Farming is a method of gaining money, with high risk but very high return. It is based on using Regrow Bloons to infinitely duplicate bloons, and can only be done in Bloons TD 5 Deluxe, Bloons TD 5 Mobile, and Bloons Monkey City and Bloons TD 5 Steam. It is based on the fact that if a regenerating bloon gains a layer it doesn't give any money when popped but if it spawns 2 bloons they will give you money when popped. Regen Farms must be started on Round 42. Monkey Lane is a good map to do it.