Board Thread:Questions and Answers/@comment-83.179.33.161-20131105065238/@comment-3153244-20131105074824

In Bloons TD Battles, you simply check the Add Regrow box.

In Bloons Monkey City (not yet publicly released), you must research Rubber Repair, after researching Fast Bloons (Yellow/Pink), Thermal Bloons (Black/White/Zebra) and Heavy Bloon Armour (Lead). Once you have researched Rubber Repair, you can choose the Regen amount when attacking someone: None, Normal (default) and Lots.