Double Gun is the 3rd upgrade of Path 3 for the Engineer Monkey in Bloons TD 6. It allows the Engineer to attack with two nailguns instead of one, allowing the Engineer to attack twice as fast alternating with each of its guns. Double Gun inherits the properties of the preceding Pin upgrade. It only affects the Engineer's nailgun and not its sentries.
Double Gun is an excellent solo for the early-game due its high pierce, decent attack speed, and stalling power via the Pin effect. Again, the Double Gun Engineer does the best along straightaways to maximize its pierce.
Generally speaking, a 2-0-3 Double Gun is better than a 0-2-3 Double Gun. The sentries have 3 pierce per shot due to the benefits of Oversize Nails crosspath with sentries, and they will deal overall more damage all-round compared to the benefits of longer range and the extra MOAB damage and Fortified damage from the Path 2 upgrades. However, 0-2-3 Double Gun is far cheaper, and works better along straight lines.
This upgrade is a helpful early-game tower for general stalling of bloons for a rather low price.
On CHIMPS, this upgrade can be useful on Geared for the early-game.
So far, there are no buffs for Double Gun itself, as all buffs for this upgrade are just inherited buffs from the previous upgrades and do not make a significant enough difference to be worthy of adding to this Version History log.
BTD6 Crosspathing (top path 1, bottom path 2)
Official upgrade artwork
Official BTD6 upgrade icon
Instamonkey icon for Double Gun
This upgrade was memed by the community, being featured in "Don't mess with my son ever again!" memes due to its design being similar to the Robo-Monkey.
Pat Fusty and the Dart Monkey have also been included in such memes due to Pat resembling an oversized version of a Dart Monkey.
Although the design and attributes are similar, the Double Gun Engineer has a slower fire rate than Robo-Monkey, but is still effective at popping Bloons.
The concept of the Double Gun upgrade is likely a reference to the Engineer from Team Fortress 2, specifically from the Meet the Engineer trailer where Engineer tells the viewers that he solves practical problems regarding self-protection with "more gun": "The answer? Use a gun. And if that don't work, use more gun."