You will encounter ADVENT Purifier early on in the game. Those guys were created to fight the Lost - every Purifier sports a flamethrower and incendiary grenades, which enables them to damage and burn their enemies. They have pretty good area of attack, which enables them to attack a couple units at a time, but poor range, which forces them to close in - making them an easy target.
Here are a few tips that ought to help you fight this enemy:
- The opponent has a chance to blow himself up upon death. It doesn't happen every time, but it's important to keep this in mind and don't send units that attack him at a short distance. If you have troops nearby, try to keep them away before you attack.
- Since they can blow up, they will be even more problematic during missions that involve the Lost - any explosion is sure to lure in a lot of them. Bear this in mind.
- This enemy has very short range; hence the most efficient way of tackling them is to order somebody with good range - a sniper or a Reaper - to take care of the problem, while keeping units with poorer range at a safe distance.
- Anti-armor projectiles will also come in handy - the enemy doesn't have much HPs, but may have as much as 3 armor points, which should enable them surviving at least one regular attack.
- Most importantly: spread your troops if you're fighting the Purifier - otherwise he'll be able to easily ignite a couple of your soldiers.