Pin

"Pins Bloons in place for a short time when struck."

- In-game description

 is the 2nd upgrade of Path 3 for the Engineer Monkey in Bloons TD 6. It allows the Engineer to pin down all affected non-MOAB-class bloons for 1.0s, similar to a stun. Pinned bloons are temporarily immobilized, and the status effect pins up to one layer, although an Engineer with this upgrade repeatedly attacking the same bloon will simply refresh the effect. Regardless of further upgrades or external buffs, this status effect cannot stop Lead or Ceramic Bloons, as these bloon types are unaffected by it.

Sentries with at least Sprockets will be able to inherit properties of the Pin effect.

It costs $185 on Easy, $220 on Medium, $235 on Hard, and $265 on Impoppable.

Summary
Pin is a valuable upgrade for early-game stalling. Combined with the Oversize Nails' pierce bonus, it makes the Engineer become quite strong along straightaways. It also is pretty cheap, making it a very good option for the early game.

Tips

 * 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, similar placements should be used for the Pin upgrade. In particular, even if the Double Gun upgrade is not purchased, the Engineer should still attack along straight lines for optimal effect.
 * The Overclock upgrade gives the Engineer a massive pierce boost, which may make the 0-4-2 crosspath a good option for applying much more pin effects to excel in the mid-game.
 * The pin effect actually prioritizes before the damage, so giving an Engineer with more damage through external buffs will actually prevent the pin effect from occurring.

Trivia

 * So far, Pin is the shortest upgrade name in the whole BTD6 franchise, along with IFR from Heli Pilot, although it is an abbreviated name and not a full name.
 * An Engineer Monkey with Pin nearby a Monkey Intelligence Bureau will still be unable to pin Leads or Ceramics. This is because the Monkey Intelligence Bureau purely changes all attack types for nearby towers to "Normal" ("Ambipopstrous" to some players). Since the Pin status effect is not identified as an attack, it does not gain the ability to affect all bloon types.