Engineer
The third Combat Shell, equipped with a Gauss Rifle primary weapon, Tarball Launcher secondary weapon, Wormlink primary ability, and Turret secondary ability. The shell also has lower self-damage.
The Engineer class can be found right before the second boss on the 4th run, completed or otherwise. On the left from the boss entrance are broken doors where you can find the combat shell lying on the operating table.
One strategy to unlock Engineer quickly is to start & abandon 3 runs, and unlock Engineer on the 4th run.
Gauss Rifle
The Gauss Rifle, also known as the XM34 CEMD Gauss Rifle in the Codex, is Engineer's primary weapon. It's an assault rifle like weapon with a large magazine, low damage, and can be effective at any range with good aim. Like all primary weapons, it can be reloaded infinitely.
It has a base damage of 20 at 300 rpm, and has 7 Weapon Mods.
Deals 20% less Weakpoint Damage for a total of 130% Weakpoint Damage.
Tarball Launcher
The Tarball Launcher, also known as the Grenade Launcher or Tarball HRGL in the Codex, is Engineer's secondary weapon. It's a grenade launcher with sticky grenades that can be detonated remotely. Like all Secondary Weapons, it has limited ammo, and cannot be reloaded.
The Tarball Launcher's explosion also gives knockback, and unlike the Rocket Launcher or Sawed Off Shotgun, it's the explosion itself that gives the knockback. This lets the player shoot down and detonate immediately to gain momentum mid-air.
Being a secondary weapon, both the base weapon and the Weapon Mods can be leveled up, and there are rare and legendary variants of each Tarball Launcher.
Wormlink
The Wormlink, also known as the Wormlink Breach in the Codex, is Engineer's primary ability. It can either hook onto a C-Ball to give a 250% movement speed boost, or can hook onto a targeted enemy, Marks & completely incapacitating, or if the enemy is killed before then, it explodes for 75 damage with a 7.5 meter explosion radius.
There is 1 HUB Upgrade and 5 Shell Upgrades related to the Wormlink.
Turret
The Turret, also known as the Sentry or Lawbringer Sentry in the Codex, is Engineer's secondary ability. It deploys a turret that deals 10 damage at 720 rpm. It both Marks and Stuns enemies nearby when deployed.
There are 3 HUB Upgrades and 5 Shell Upgrades related to the Turret.