In the game mode Mann vs. Machine, a common challenge for an Engineer is dealing with Sentry Busters, preventing them from detonating near buildings and friendly teammates.

There is specific logic of when Sentry Busters arrive. This guide illustrates how to take advantage of that logic, allowing your team one less challenge to worry about. The information in this guide will greatly reduce any challenges Sentry Busters have to offer when playing as an Engineer.

Sentry Busters are NOT inevitable when playing as an Engineer, meaning they can be avoided. By strategically placing your buildings, you can go an entire game without seeing a single one! Here's the secret:

Sentry Busters appear when your Sentry Gun reaches a certain kill or damage threshold. This kill threshold is dependent on mission and difficulty, and the exact number is located in the population files for each mission. Generally speaking, the kill threshold across all missions is between 25-35 kills.

Have you placed your sentry near the front lines, such as in one of these common locations?











If so, chances are that you encounter Sentry Busters very early in the wave!

The above locations aren't necessarily bad, however they provide an unnecessary challenge and risk of dealing with Sentry Busters. Though these are common locations, there are definitely better ones! To determine where the best spot is, you must have a perfect knowledge of two things:

1- The bomb carrier's path
2- Where exactly your team is defending

Knowing these two things, the best location for your sentry is in a place where it only fires when your team begins to be overwhelmed, and is in the bomb carrier's path. If your sentry is too far forward, you'll get Sentry Busters early in the wave. If your sentry is too far back, your sentry won't support your team in case of overwhelm, causing them to die. This would leave your sentry quite vulnerable, since your team would not be able to defend it. If your sentry is not in the bomb carrier's path, they can slip by your defenses with relative ease. Here's some additional details to the above crucial points:

• The bomb carrier's path: Before the start of every wave, the bomb carrier's path is clearly outlined in blue holographic arrows. Every wave or attempt changes the bomb carrier's path, which means you will want to re-evaluate your sentry gun position whenever you beat or fail a wave.
  
• Where exactly your team is defending: Coordinate with your team on which choke point they'll hold, and put your dispenser there to support them. Your dispenser governs where your team will hold, which makes your team's defense location easy to identify.

NOTE: These are NOT the best places under every circumstance! These are simply examples based on the above criteria. I counted at least three good places to defend for every bomb carrier path, so take these examples at face value.


This sentry location is good because it supports your team when robots get too close, and it covers a good portion of the enemy path.


Note that this Sentry Gun isn't that far away from a "Sentry Buster" placement. It provides cover to the defending position when robots close in, and it covers a good chunk of the bomb carrier's path.


Similar to the other examples, the sentry provides cover when robots get too close, but otherwise won't fire. Both the sentry and dispenser would be in vastly different locations with a different bomb carrier path.


There's a tiny buildable spot on the rocks there for the dispenser, letting your team defend both on the rock and around the corner. In case enemies start to turn the corner, your Sentry Gun is ready to fire and help defend your teammates.

Sometimes your team has a difficult time defending their location, and despite its good location, will still rack up enough kills to attract a Sentry Buster. When this occurs, you get to make an important and situational choice:

- Do I lure the Sentry Buster away from the team and trick it into detonating? or;
- Do I abandon my Sentry and consciously let it get destroyed?

Some details on each choice, as they come with pros and cons:

• Trick the Sentry Buster: This tactic is quite common; picking up your gun, running towards the Sentry Buster, and backing away when it starts to detonate. Keep in mind that though you may have tricked that Sentry Buster, another will immediately take its place. In fact, you will get a constant stream of Sentry Busters until that particular Sentry Gun is destroyed or until the wave ends.
  
• Abandoning your sentry: This might sound like a heartless and stupid thing to do, but can potentially be a smart move because your kill threshold is reset to zero when a Sentry Buster destroys your gun. If you have an Upgrade Buildings canteen, you can immediately replace it with little to no delay. If your team has regained control of the choke point, you could even rebuild and re-upgrade your sentry manually. Investing upgrades in Wrench swing speed can notably decrease the time it takes to get your sentry back up to level 3.
  
  Note that intentionally destroying your sentry with the Destruction PDA does not count - it must be killed by a Sentry Buster for the kill threshold to be reset.

When Tanks come, this is your Sentry's time to shine. Tank damage does not count toward your sentry's kill threshold. This means that if a Sentry Buster is not currently in play, you can focus on the Tank without worrying about them. Take advantage of this fact and take your Sentry to the front lines, using the wrangler to focus its increased fire rate directly on the Tank.

As the Tank passes your choke point, coordinate with your team whether they want the dispenser to stay at the choke point, or want it to follow the Tank with you and your sentry. This choice usually depends on whether there are other robots accompanying the Tank. Take your dispenser with you if the Tank is chugging along by itself. If you're able to place your dispenser within your Heavy's or Pyro's range while they're point-blank with the tank, they don't have to stop for ammo, greatly increasing your team's damage per second (DPS).

The main principles this guide intends to explain is the following:

• Sentry Busters appear only when your Sentry Gun reaches a certain kill or damage threshold.
  
• Set your Sentry Gun slightly behind the front lines, allowing your team to dish out most of the damage. Your Sentry is best utilized as a backup and support to your teammates.
  
• If you exceed the kill threshold and a Sentry Buster does arrive, letting it destroy your sentry resets the threshold to zero. If not, you will continually get Sentry Busters until that gun is destroyed or the wave ends.
  
• Dealing damage to Tanks does not affect the kill/damage threshold, so focus on them as much as possible.

Have feedback or additional thoughts for this guide? Feel free to leave them in the comments!