Sentry Gun

Sentry Gun lets the Engineer Monkey place a sentry somewhere in its range every 10 seconds. Each sentry lasts 25 seconds (30 with Vigilant Sentries), shoots every 0.95 seconds, hits up to 2 Bloons per shot and has 45 range. Without buffs you will usually have two or three sentries out at once. The Engineer tries to place them where they cover a good piece of track.

Crosspaths change new sentries: Larger Service Area adds range, Deconstruction adds MOAB and Fortified damage, Cleansing Foam lets them strip properties, Oversize Nails adds pierce and lets them pop Frozen Bloons, and Double Gun makes them fire two shots.

When to buy it

Sentry Gun is a solid early-game option on compact maps where the sentries all land near the same stretch of track, such as Workshop. On maps with many separated track sections, sentry placement is more random and less efficient. It takes time to build up a full set of sentries, so do not rely on it right after placement.

It leads to Faster Engineering and the whole top path, and as a crosspath it adds sentries to 1-0-3 Double Gun and 1-0-4 Bloon Trap builds.

Is it worth it?

Yes as the first step of the top path and on the right maps. For pure early damage on spread-out maps, a Boomerang Monkey is often simpler.