Bloons get pushed backwards or slowed after each hit.
~ BTD6 descrpiton
Knockback is the first upgrade of Path 3 for the Super Monkey in Bloons TD 6. It gives the Super Monkey the capability to push back or slow down bloons on each hit. The Knockback upgrade costs $2550 in Easy Difficulty, $3000 in Medium, $3240 in Hard, and $3600 in Impoppable. It will push back bloons below Ceramics, stuns ceramics, or slows down MOABs and above (except the BAD, which cannot be slowed at all).