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The Monkey Engineer is a tower in Bloons TD 5 Deluxe, Bloons TD Battles Mobile, Bloons TD 5 Mobile, and Bloons Monkey City. It wields a nail gun that shoots at a quick speed, popping three bloons per shot. With upgrades, the Monkey Engineer can spawn sentries, assisting it with popping power. This is one of the most reliable starting towers in the game and with the help of its sentries, it can solo multiple rounds early on.

In Bloons TD 5, it was first released on Bloons TD 5 Deluxe on first release, along with Bloonchipper. It was later added to Bloons Monkey City Flash on September 2014 (?). Later, it was released on all mobile versions of the game. It was never added to Bloons TD 5 Flash or Bloons TD Battles Flash.

An update on Bloons Monkey City on 15th October 2014 added Monkey Engineers and Second City simultaneously. Engineers are unlocked once you reach level 5 on your second city.

The Engineer Monkey was added to Bloons TD 6 on September 17, 2019 as part of the 12.0 update. For more information, see Engineer Monkey.


Path 1[]

Sentry Gun Icon BTD5
Sentry Gun
COST: $425 / $500 / $540 / $600

Description: Automatically creates sentry guns and deploys them on the ground nearby. Sentries shoot sharp steel pins at the bloons but only last a short time.
Effect: Self-explanatory
Faster Engineering Icon BTD5
Fast Engineering
COST: $340 / $400 / $430 / $480

Description: Engineer increases his build speed, producing sentry guns more often.
Effect: Engineer creates sentries TBA% faster.
Cleansin Foam Icon BTD5
Cleansing Foam
COST: $680 / $800 / $865 / $960
UNLOCK: 3,200 XP

Description: Engineer uses a special dispenser to spray down the track with a cleansing foam that removes camo and regen properties. Also pops lead bloons.
Effect: Self-explanatory
Bloon Trap Icon BTD5
Bloon Trap
COST: $2,975 / $3,500 / $3,780 / $4,200
UNLOCK: 8,000 XP

Description: Creates a powerful bloon trap that destroys all the bloons caught in it. Once full, trap will destroy itself after a short time. If emptied manually, gives you extra cash. Only one trap can be active at a time.
Effect: Self-explanatory

Path 2[]

9-Inch Nails Icon BTD5
9-Inch Nails
COST: $380 / $450 / $485 / $540

Description: Engineer's nailgun upgrades to shoot massive 9-inch nails that can pop 8 bloons at once including frozen bloons.
Effect: Self-explanatory
Larger Service Area Icon BTD5
Larger Service Area
COST: $550 / $650 / $700 / $780
UNLOCK: 1,000 XP

Description: Engineer can shoot further and deploy sentries in a larger area.
Effect: Engineer's range increased by TBA%.
Sprockets Icon BTD5
COST: $465 / $550 / $595 / $660
UNLOCK: 3,300 XP

Description: Adding sprockets to sentries and the nailgun increase their fire rate appreciably.
Effect: Self-explanatory
Overclock Icon BTD5
COST: $11,475 / $13,500 / $14,580 / $16,200
UNLOCK: 11,000 XP

Description: Activated Ability: Overclock - target tower becomes super powered for 60 seconds.
Effect: Self-explanatory

Total Costs[]

Differences Between BTD5 Flash and BTD5 Mobile[]

Technically speaking, Monkey Engineer only appears in Bloons TD 5 Deluxe, Bloons Monkey City, and all mobile versions of the Bloons TD franchise. However, there are several differences between the Engineer in Flash games (i.e. BTD5 Deluxe and BMC Flash) than in mobile versions of the games.

  • BUFF Bloon Trap no longer loses collection value in later rounds.
  • NERF The Monkey Engineer is unlocked at Rank 21 instead of Rank 20.
  • NERF Sentry Gun costs more ($450 → $500).
  • NERF Faster Engineering costs more ($350 → $400).
  • NERF Cleansing Foam costs more ($750 → $800) and no longer has unlimited pierce.
  • NERF Bloon Trap costs more ($3000 → $3500) and Monkey Farmers cannot collect full traps.
  • NERF If an Overclock is sold, the tower boosted by that Engineer will lose the boost effect while still showing the aura.
  • Change Pops from the Monkey Engineer's Sentries, Cleansing Foam, and Bloon Traps now count towards the total pop count of the Engineer.
  • Change Bloon Traps now are emptiable after each round, even when Non-Stop Mode is on. This is not the case in BTDB Mobile, Apopalypse Mode, and Monkey vs Monkey.
  • NERF Bloon Traps no longer detect Camo unless the tower is granted Camo detection.
  • Change Sentries made by an Engineer automatically disappear when the Engineer is sold.
  • BUFF In desktop versions of the games, Bloon Traps only have to be hovered over to be collected, rather than having to manually click on them.

Version History (Bloons TD Battles Mobile)[]

Engineer is in a weird state where he can carry you for a long time by spamming sentries, but he is not overpowered either. Despite this, he is sometimes given a few buffs to make him more popular.

Engineer is generally not very popular in normal games (the only semi popular loadouts that use it are Engineer Farm Ninja and Engineer COBRA Apprentice), but it is a quite popular tower in Play With Fire. This is especially the case when utilising the Bloon Trap upgrade for effectively increasing income two-fold (both by bloon income, and from filling up Bloon Traps from sending bloons that will go back to you).

  • BUFF Bloon Traps no longer spawn on unused track in Defend Mode.
  • BUFF Overclock price decreased ($13500 → $11000).
The Engineer is a good tower with decent use-rates, but we hope to encourage players to use the Overclock ability rather than the (more popular) Bloontrap with this change.
~ "BTD Battles Update 4.1 - Big Balance Changes Incoming!"
  • BUFF Overclock price decreased ($11000 → $7500).
Much like the Heli-Pilot, this change means that you'll now need to wait the full cooldown period before using the ability again.
~ "BTD Battles Update 4.3.1 Balance Changes"
  • NERF Double-speed-tower ability cooldown timer of Overclock now starts upon tower selection, rather than as soon as the screen opens.
We think the Engineer is pretty well balanced overall, but we've tweaked a couple of prices to bring them more in line with the power of the upgrade.
~ "BTD Battles Update 4.6 Balance Changes"
  • BUFF Larger Service Area price decreased ($650 → $500).
  • BUFF Cleansing Foam price decreased ($800 → $650).
  • Change Larger Service Area additional range decreased by 50% (debatable buff/nerf among fans, since Larger Service Area usually does worse for them than it helps to them).
We feel like the Engineer is a solid tower, but might be slightly too expensive for what you get. A slight tweak of its base cost, and the cost of it's [sic] Larger Service Area upgrade, should give it that bit more value. We've also reduced the price of the Overclock ability since it's less powerful than it is in BTD 5 for the same cost.
~ "BTD Battles Update 4.9 Balance Changes"
  • BUFF Tower price decreased ($450 → $400).
  • BUFF Larger Service Area price decreased ($500 → $475).
  • BUFF Overclock price decreased ($7500 → $6000).
  • NERF Bloon Trap costs more ($3500 → $3800)
  • NERF Bloon Trap manual collection multiplier reduced (2.0x → 1.8x), and manual collection income decreased ($1 → $0.8). Automatic collection remains unchanged.
  • BUFF Larger Service Area cost decreased ($475 → $200)
  • BUFF Sentries no longer have a footprint, allowing towers to be placed on top.
  • NERF Bloon Trap manual collection multiplier reduced (1.8x → 1.3x), and manual collection income decreased ($0.8 → $0.3). Automatic collection remains unchanged.
  • BUFF Sprockets attack cooldown reduction increased for Engineer (-30% -> -50%) and deployed sentries (-40% -> -50%)
  • NERF Tower price increased ($400 → $450).
  • BUFF Fast Engineering sentry production cooldown decreased (6s → 5s).
  • BUFF Fast Engineering price decreased ($400 → $350).
  • NERF Bloon Trap manual collection multiplier reduced (1.3x → 1.1x), and manual collection income decreased ($0.3 → $0.1). Automatic collection remains unchanged.
  • BUFF Cleansing Foam price decreased ($650 → $550).
  • BUFF Overclock price decreased ($6000 -> $5200)


Monkey Engineers have a number of useful mechanical tools to pop bloons and even remove camo or regen properties. Powerful upgrades include: Cleansing Foam, Bloon Trap, Overclocked.
~ BMC Flash description



  • There is a glitch with the 3-X Monkey Engineer's cleansing foam that if it's engineer is under the range of a X-3 Monkey village the cleansing foam will pop all bloons, not just leads. Same effect with tier 3 specialty building.
  • The Monkey Engineer can build Sentries on the track in BMC Mobile.
  • The Monkey Engineer was added in the Bloons TD 5 Mobile 1.3 update, along with a new track.
  • In BMC, the 9-inch Nails upgrade costs $700, but in the other games and levels, it costs $450.
  • This tower can be upgraded to use Sentry Turrets (That randomly spawn within his range) and use a Soap Dispenser to spawn foam that removes camo and pops lead. The Sentry Turrets and Dispensers are most likely references to the game Team Fortress 2.
    • The tower itself may also be a reference to the Engineer class in Team Fortress 2, and with the blue colours from the second upgrade on path 1, the Monkey itself resembles a BLU Team Engineer from Team Fortress 2. The red colours from the second upgrade on path 2, the Monkey itself resembles a RED Team Engineer.
    • The icon for a 1/0 Monkey Engineer also seems to be a reference to Team Fortress 2, as its icon is the engineer hollering and striking a sentry violently with a wrench.
    • Probably to avoid either a bad pun or seeming too much like Team Fortress 2, the engineer does not wield a Monkey Wrench, but rather a crescent wrench.
    • The first upgrade in path 2 is a reference to the industrial band, Nine Inch Nails .
    • The super sentries take the reference to the next level. Since they are red and larger, they look much more similar to the red engineer's sentry gun.
    • Another possible reference to the game is its second fourth tier upgrade, although it actually is not an Engineer's ability.
  • A Monkey Engineer with Cleansing Foam doesn't aim with his gun, so the foam can come from behind the monkey.
  • In the mobile games, sentries can appear anywhere, even on the road, water, trees, other sentries, even other towers. In the other games, they only do this when there's no more room for them.
    • They also lose their footprint in BTD6.
  • Monkey Engineer's 1-0 or 2-0 upgrades (sentries) can be considered as a burden to all towers (also includes himself), as it take up spaces so that you have to either sell it or wait until it's gone to place towers on the spot it occupies.
  • They are mentioned in the description of Hotter Cooldowns, even on flash.
  • This tower with the Cleansing Foam upgrade (besides the Monkey Sub's: Bloontonium everlasting ability) is the only tower that makes Regrowth Bloons lose their regen status.
  • A Support Chinook can move Sentries.
  • The tank for the Cleansing Foam is the same as the tank a Glue Gunner has with the Glue Striker upgrade.
  • Spamming 2-3 Engineers or 3-0 while their third tier Specialty Building is activated can beat every single track on Easy, including the Extreme Tracks, if some are influenced by a 2-2 Monkey Village.
  • This is the recommended tower to use in the special mission Full House, as it will deploy sentries when there can be no more towers placed, allowing the player to bypass the maximum amount of towers. This also applies to Random Missions where the Monkey Engineer is available.
  • In Bloons TD 5 Deluxe, a glitch may occur; if an engineer cannot shoot a bloon before the bloon is popped, the engineer may shoot in the direction it is facing without changing direction.
  • Another BTD5 Deluxe glitch involves clicking on a Sentry Gun blanking the artwork. Also, the Go button never shows up and the game cannot continue.
  • The engineer actually has his artwork wrong; when you upgrade the Monkey Engineer to X-2, the icon next to his pop count will appear with the grayish hat for an X-3 Engineer. When you upgrade to X-3, the icon will appear with the red hat for an X-2 Engineer.
  • If the player sells the engineer, his sentries would be gone instantly after selling the engineer (Mobile only).
    • However, any Cleansing Foam from the engineer will remain its full duration.
    • This is not true in Bloons Monkey City Web as both the foam and the sentries will stay its full duration.
  • In earlier versions of the Mobile versions of BTD5 and Bloons Monkey City, a 1-4 Engineer will look like a 0-0 Engineer with the yellow hardhat and no wrench, but a 0-4 and 2-4 Engineer will have the gray hat and the wrench. It has been corrected in Version 1.8.
  • The Engineer and the Spike Factory both use sprockets in their upgrade descriptions.
  • In Bloons Monkey City Mobile, there is a special mission where you must rescue 5 Monkey Engineers by paying $450 each. Engineer cages that have been touched by bloons will make them disappear and not be able to be used in the game. The objective is to rescue at least one Engineer and beat all the rounds in order to unlock it in the player's city.
  • In BMC, when you have Monkey Knowledge of Rank 3 (camo-shooting sentries) they lose their camo detection after upgrading the Engineer to Sprockets.
    • One reason might be that the Sentries are named "SentrySprockets". This could be an indication that they are considered to be a different tower and thus are unaffected by monkey knowledge. This does not happen in BMC mobile.
  • In BMC, the Monkey Engineer pop count only applies to the engineers themselves, however, BMC Mobile's Monkey Engineer pop count applies to every gadget made by the Engineer, that is, the Sentries and Bloon Traps.
  • Sentries inside the range of a Monkey Village will have the effects of it, regardless of whether the Engineer that spawned them is inside the range of the Monkey Village.
  • In Fast-track mode in BTD5 the Engineer will take a long time before building any sentries on the first round which can cause issues if the player primarily uses them.
  • It is possible to beat Impoppable Mode in BTD5 with only Engineers and Super Monkeys.