Sentries deploy with different damage types based on your need.
~ BTD6 description

Sentry Expert is the 4th upgrade of Path 1 for the Engineer Monkey. It allows the Engineer to create specific sentries that specialize in popping specific bloon types. There are four unique sentry types that may spawn from the Sentry Expert, each with unique attacks: Crushing, Boom, Cold, and Energy. The Engineer may produce specific types depending on what bloons spawn within or near its radius. There is no manual control over what sentry types may or may not spawn.

When no special Bloon types are present with the Sentry Expert's range, the Sentry Expert cycles between Crushing, Boom, Cold and Energy Sentries in that order. If there are certain bloon types detected within the Engineer's radius, he will skip certain sentry types in the sentry-spawning cycle unless there are other bloon types detected within his radius where certain sentry types must be spawned. For example, a Boom Sentry will not spawn if Blacks exist in the Engineer's radius, but can still spawn if Leads also appear in range of the same Engineer.

Sentry Expert costs $2125 on Easy, $2500 on Medium, $2700 on Hard, and $3000 on Impoppable.

Types of Sentries[edit | edit source]

There are four types of sentry that the Engineer may produce. All sentry types despawn after 25 seconds. (30 with Vigilant Sentries MK) All Sentries have 50 range and gain +4 range with Larger Service Area and +1 pierce with Oversize Nails.

Crushing Sentry[edit | edit source]

Crushing Sentry

The crushing sentry appears red and shoots spiked balls reminiscent of the Dart Monkey's top path upgrades, having both the bounciness and the same amount of pierce as Spike-o-pult. These balls deal 2 damage to Ceramic Bloons and are able to bounce off obstacles. It has a very slightly greater attack speed than Spike-o-pult.

Damage: 1 (+1 to Ceramics)
Pierce: 22
Attack Speed: 1.0x (every 1.0s)
Damage Type: Shatter Type (pops Black, White, Purple, Frozen) Shatter

Does not spawn if Lead Bloons are within range of the Engineer, unless Blacks or Whites are within range of the same Engineer, but it will spawn if there are Ceramic Bloons nearby.

Energy Sentry[edit | edit source]

Energy Sentry

The energy sentry appears yellow and shoots laser blasts reminiscent of the Super Monkey's Laser Blasts upgrade. It has the highest attack speed, however the lowest pierce of any sentry. Laser blasts can pop frozen bloons but cannot pop Leads or Purples. It attacks a lot slower than Laser Blasts but deals 2 damage each.

Damage: 2
Pierce: 4
Attack Speed: 1.75x (every 0.57s)
Damage Type: Energy Type (pops Black, White, Frozen) Energy

Always skipped (does not spawn) if there are Purples. Also does not spawn if Lead Bloons are within range of the Engineer, but may still appear if Blacks or Whites are within range of the Engineer.

Cold Sentry[edit | edit source]

Cold Sentry

The cold sentry appears blue and shoots snowballs reminiscent of the Ice Monkey's Cryo Cannon upgrade. Affected bloons are frozen for 1.5s and also gain the Permafrost effect. Snowballs pop and freeze bloons in a small radius, with a blast radius of roughly ~10. Cannot affect Whites, Zebras, or Leads. The cold sentry roughly acts like a weaker 1-0-3 Cryo Cannon.

Damage: 1
Pierce: 15
Attack Speed: 0.67x (every 1.5s)
Damage Type: Cold Type (pops Black, Purple) Cold

Does not spawn if White Bloons or Zebra Bloons are within range of the Engineer, but will spawn if there are Black Bloons or Lead Bloons (even though it cannot damage Leads).

Boom Sentry[edit | edit source]

Boom Sentry

The boom sentry appears black and is slightly larger than other sentries and shoots bombs reminiscent of the Bomb Shooter. Bombs pop bloons in a small radius (18 radius, roughly slightly less than the Ice Monkey's base range) and can pop frozen Bloons and Lead Bloons. The boom sentry roughly acts like a weaker 1-1-0 Bomb Shooter.

Damage: 2
Pierce: 30
Attack Speed: 0.77x (every 1.3s)
Damage Type: Explosion Type (pops White, Purple, Lead, Frozen) Explosion

Does not spawn if Ceramic Bloons, Black Bloons or Zebra Bloons are within range of the Engineer, but will spawn if there are Lead Bloons or White Bloons nearby.

Strategy[edit | edit source]

Summary[edit | edit source]

Sentry Expert is a situational upgrade for upgrading the sentries. On certain aspects, it can be less powerful, due to the fact that most of the Engineer's special sentries attack considerably slower, with exception of Energy Sentry. On other aspects, it can be pretty helpful, as most of the special sentries utilize a combination of utility and extra overall damage in some way shape or form. Overall, Sentry Expert is a relatively underpowered upgrade, mainly due to how unreliable the sentry-spawning algorithms are.

Certain sentry types can be very useful in different situations:

  • Energy Sentries are powerful against damaging MOAB-class bloons and popping up bloons for a rather low price.
  • Cold Sentries are helpful at stalling Ceramics, especially Super Ceramics, a feature that Pin is unable to do. However, they can be more harmful than good in situations where most of the defense consists of sharp-based projectiles.
  • Crushing Sentries have immense popping power and can work effectively in locations with poor Line of Sight, as the ball projectiles are able to bounce off walls, similar to Spike-O-Pult.
  • Boom Sentries allow popping of Leads and deals a considerable amount of damage to dense clumps of bloons. They can also deal decent cleanup against weaker clumps of bloons.

However, there is very limited control over the Sentry Expert's production of certain sentry types. As such, it can become a hassle for the Sentry Expert to produce the right combination of special sentries that will become the most favorable to your given situation.

Tips[edit | edit source]

  • Just like Laser Blasts, the Energy Sentry can't pop Lead or Purple Bloons.
  • Similar to totems, sentries cannot be buffed by Alchemists. Buffing the Engineer will not buff the Sentries, but it will improve the production rate of sentries.
  • The Crushing Sentry deals double damage to Ceramic Bloons but can't pop Lead Bloons.
  • Even though it cannot affect them, cold sentries will still spawn if there are Lead Bloons.
    • There is a bug/special case where only cold sentries will spawn when there are DDTs present.
  • Because all sentries benefit only from Tier 1 crosspaths, crosspathing Sentry Expert has little benefit for the sentries, although the +1 pierce benefits from the Oversize Nails crosspath helps fairly well for Energy Sentries. However, it should be noted that Larger Service Area upgrade crosspath should only be used when there is little space to place new sentries. Usually, 4-0-0 Sentry Expert should suffice, and crosspaths only really matter for helping the main Engineer himself.
  • Crushing Sentries can be somewhat helpful on maps with many obstacles, such as Cornfield.
  • Adding a small group of Sentry Experts can handle Round 63 adequately, as well as deal adequate stalling on late-game rounds via the Cold Sentries.

Update History[edit | edit source]

  • Buff.png Energy Sentry damage increased from 1 → 2
  • Buff.png Boom Sentry damage increased from 1 → 2
  • Buff.png Boom Sentry attack rate increased from 1.5 → 1.4
  • Buff.png Crushing Sentry attack rate increased from 1.25 → 1
  • Buff.png Sentry Expert price reduced from $2800 to $2500
  • Buff.png 4xx Sentry Expert's Boom Sentry blast radius increased 12 -> 18
  • Buff.png 4xx Sentry Expert's Boom Sentry attack rate increased 1.4s -> 1.3s
  • Buff.png Sentry Expert is now affected by crosspathing from Larger Service Area and Oversize Nails.
  • Buff.png Sentry Expert sentries are deployed faster (7s --> 6s)
  • Buff.png Sentry Expert base sentry range increased (45 --> 50)

Gallery[edit | edit source]

Projectiles[edit | edit source]

Trivia[edit | edit source]

  • Sentry Expert's upgrade icon features all four types of Sentries that the Sentry Expert can create.
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