I don't think they trigger off proximity but don't quote me on it. If an enemy is near one and you shoot it, it will explode the next turn. I thought these things hatched to spawn more enemies. I had a vehicle act as a shield while one person did the injections. Once you start injecting it takes 2 full turns to fulfill the action so you can't rush it.

There's 4 spots you need to inject to end the mission. Once you land on him you will be randomly split into 2 teams.

FYI you need to fly to a haven he is targeting, wait for him to get there, click on your plane and there should be a symbol at the bottom to board the behemoth. The project also unlocks a virophage aircraft gun which is kind of useless once you kill behemoth. Even with multiple planes I had a hard time driving it off once it started sending in the big ships. Which sucks because it will destroy havens if left unchecked. You practically have to get to the end of the game to be able to kill it. It's literally an ordinary manticore covered in flesh but it can hold 2 more passengers. Then you have to build said manticore to be able to attack the Behemoth. You have to research virophage to get the research to make the masked manticore. Like 21% by the time I killed the bastard. Then I built a main base in Europe to help save the few remaining havens because I was running low. I then setup shop near the north pole just so I had a quicker way to Europe. I eventually went across Alaska to Asia for story missions. Once I had 2-3 planes I pretty much had south america, mexico and north america covered. If you build a base over there the flyers might destroy it. If you fly there your leaving your homeland defenseless. If he attacks the other side of the world where you have nothing just don't bother. Let a shot land and stick around for as long as possible to let the fire dmg destroy all the guns. Basically pray to the dead god you get in close before their weapons destroy your missiles.

The security system can fend off bio weapons(assuming they don't blow it up first) and fire damages EVERYTHING. Invest in Anu Blimps, security station and Incendiary weapons. I figured id make this topic because I haven't found much info on this dlc. Only took me 3 playthroughs due to havens being destroyed.

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