The Engineer is a unique class that has no equivalent in vanilla XCOM, though they borrow some elements from the Grenadier Heavy and Support classes. Engineers are specialized in the use of grenades, with their starting Grenadier ability giving them two uses of each damaging grenade item they carry, and a bonus to grenade throwing range, and have several more perks to improve grenades further. Engineers also have access to perks improving their ability to destroy cover, and improving their use of the arc thrower.
Grenadier Allows 2 destructive grenades in a single inventory slot, and the soldier may throw grenades 20 percent further.
No other bonuses.
Lance Corporal
Rapid Reaction Confers a second reaction shot, if on Overwatch and the first reaction shot is a hit.
Smoke Grenade Deploy a smoke grenade once per mission. The smoke confers +20 defense to all units, not just allies, and lasts through the enemy turn. Taking the perk on level up also allows an additional action after deploying a smoke grenade.
Sapper Your grenades do additional damage to enemies, and all your weapons do additional damage to the environment(+1 damage with AP and HE grenades, +2 damage with Alien grenades and triple environmental damage for all weapons).
Provides +2 Aim.
Provides +1 Aim
No other bonuses
Corporal
Sharpshooter Bonus +10 Aim against enemies in full cover, crit chance +10% against all targets.
Dense Smoke Smoke Grenades have increased area of effect and further increase units' Defense by 20.
Holo-Targeting Shooting, flushing or suppressing enemies also confers a +10 Aim to any allies' attacks on those enemies.
Provides +2 Aim.
No other bonuses.
No other bonuses.
Sergeant
Ranger Primary weapons do one additional damage.
Smoke and Mirrors Allows one additional use of all support grenades during each mission. It also increases charges from Smoke Grenade and Battlescanner perks by 1.
Repair Confers +2 charges for Arc Throwers.
Provides +1 Mobility.
Provides +1 Mobility.
Provides +1 Mobility.
Tech Sergeant
Suppression Can fire a special shot that grants reaction fire at a single target. The target also suffers a -30 Aim penalty and reduces the range of all AOE attacks.
Battle Scanner Grant 2 Scanning devices. When thrown creates a new source of vision for 2 turns.
HEAT Warheads Rockets and Grenades do 50% extra damage to robotic enemies.
Provides +1 Will.
Provides +1 Aim.
No other bonuses.
Gunnery Sergeant
Will to Survive Reduces all normal damage taken by 1.5 if in cover and not flanked.
Ready For Anything If the unit fires without moving, it automatically enters overwatch.
Packmaster All limited-use items in your inventory receive one extra use.
Provides +2 Will.
Provides +2 Aim.
No other bonuses.
Master Sergeant
Extra Conditioning Confers bonus health based on which type of armor is equipped. Heavier armor increases the bonus.
Fire Rocket Fire a high explosive rocket using an equipped launcher.
Bombardier Throw or launch grenades over exceptionally long distances(+50%).
Provides +3 Aim +3 Will +1 Mobility.
Provides +2 Aim.
No other bonuses.
Stat Progression
Rank
HP at level
Total HP
Aim at level
Total Aim
Specialist
1
1
2
2
Lance Corporal
0
1
2
4
Corporal
1
2
2
6
Sergeant
0
2
2
8
Tech Sergeant
1
3
2
10
Gunnery Sergeant
0
3
2
12
Master Sergeant
1
4
2
14
Tactical Advice
Role: Offensive Support / Defensive Support
Engineers are a class largely based around items and special abilities. Their starting Grenadier perk allows them doubled offensive grenades and a throw range bonus, and they can boost their offensive grenades further with Sapper and Bombardier. With perks such as Smoke Grenade, Dense Smoke and Smoke and Mirrors, Engineers can also become extremely proficient with defensive grenades, such as smoke grenades, ghost grenades and flashbangs, since the range bonus from Grenadier and Bombardier applies (Bombardier even works with Battlescanners, which are also available as a perk). Engineers can also enjoy triple uses of the Arc Thrower with the Repair perk. Unfortunately, all of these roles compete for your limited item slots.
If you choose the Fire Rocket perk, note that you will be unable to select a sidearm any more. Also bear in mind that Rocket and Shredder Rocket items are restricted to the Rocketeer class, so an Engineer with a rocket launcher can only ever have the one rocket. On the other hand, with Sapper that one rocket will blow a very big hole in any cover you fire it at.
On the downside, Engineers have the worst aim progression of all classes, so should you manage to exhaust your special abilities Engineers are lacking in offensive ability. Their dependence on items means Engineers are hard pressed to spare an item slot for a defensive item such as Chitin Plating, which, since they need to be near the front to throw their grenades at enemies, can leave them a little lacking in defense.