Board Thread:Questions and Answers/@comment-205.250.45.87-20150220073622/@comment-26109599-20150220154226

This isn't a glitch: After a certain point in the game, the bloons change. All bloons go slightly faster each round, and the MOAB class bloons gain some health each round. The ceramics' health goes from 10 hits to destroy to 38 hits to destroy. Also, ceramics only release one rainbow, rainbows only release one zebra, etc. This ramp in difficulty is designed to keep players from reaching potentially infinite rounds. In contested territory, it generally happens after the final milestone. It also happens in BTD5, when the player starts freeplay mode.