Pins Bloons in place for a short time when struck.
~ BTD6 description
Pin is the 2nd upgrade of Path 3 for the Engineer Monkey. It allows the Engineer to pin down all affected non-MOAB-class bloons for 1.0s, similar to a stun. Pinned bloons temporarily fully stop the bloon from progressing, and the pinning effect affects up to one layer, although an Engineer with this upgrade attacking the same bloon again will simply refresh the effect. Regardless of further upgrades, this status effect cannot stop Lead Bloons or Ceramic Bloons, as these bloon types are completely unaffected by them.
It costs $185 on Easy, $220 on Medium, $235 on Hard, and $240 on Impoppable.
When further upgraded to Double Gun, it become quite useful against normal bloons.
It is best not used after Round 81, as Super Ceramics are generally the only non-MOAB-class bloons that will appear on those rounds.
Because this upgrade inherits extra pierce from the previous Oversize Nails upgrade, use similar strategies for the Pin upgrade. In particular, if going without the Double Gun upgrade, the Engineer should attack along straight lines for optimal effect.