Board Thread:Questions and Answers/@comment-80.60.239.190-20150811212453/@comment-26109599-20150811230548

Starting at round 50, the cash gained from each bloon decreases. It does so every ten rounds until you get no more than $50 from a MOAB and its children by Free Play. If you want to get really far in Free Play, get some high level Banana farms and farm the crap out of them.

Also, about RBE: when there are MOAB-class bloons in the round, the RBE includes all the hits it takes to destroy them. For example, a ZOMG has an RBE of 16,656, even though there is the equivalent of only 6,080 non-MOAB-class bloons contained within it.