Lieutenant

Lieutenants are a type of enemy in the game Batman: Arkham City. There are only 2 known enemies labeled as "Lieutenant", namely Mr. Hammer and Sickle.

Militia Brutes in Batman: Arkham Knight may also be identified as "lieutenants", but as an enemy type, they're still only "Brutes".

Physical appearance
Mr. Hammer and Sickle, known collectively as the Abramovici Twins, are Russian-born men, with unusually large stature within City. They are separated conjoined twins and each only have 1 arm, but they're still strong and nimble enough to wield large weapons, namely a large hammer and a large sickle. Mr. Hammer and Sickle serve as Lieutenants for Joker and Penguin respectively.

Combat capabilities
Lieutenants are considered the 2nd most dangerous type of enemy for their large stature and damage dealing capability, 2nd to Titans. Lieutenants mainly attack by using their large weapons. Unlike Titans, they can't run and charge, but instead simply leap great distances to approach your character for an attack. However, their attacks tend to be slow and easy to dodge.

Mr. Hammer attacks by pounding with his hammer. Sickle, on the other hand, by sweeping his surroundings with his sickle, which makes him slightly more dangerous because his attack has broader range.

Strategy
Lieutenants can be dealt with with a variety of combat moves and gadgets. The following gadgets can be used on them:
 * The Batclaw can be used grab onto a Lieutenant's hand, and as your character pull it, the Lieutenant will sweep his weapon around, causing "Collateral Damage" by hitting other enemies in the way, which rewards 10 points per hit enemy. You should make sure to stay far enough from him, though.
 * You can shoot a Remote Electrical Charge at a Lieutenant, which also causes him to sweep his weapon around.
 * A Freeze Blast can immobilize a Lieutenant for some time, which gives you time to deal with other enemies. However, the ice will break as soon as as you hit him.
 * Caltrops don't inflict significant damage, but they can slow down a Lieutenant if he steps on them and has to remove them from his feet.

Apart from the gadgets above, only 4 types of combat move are effective against Lieutenants:
 * The most common move is a Beatdown. You can immediately do a Beatdown on a Lieutenant without a Stun as with other types of enemies. Each Beatdown Strike on a Lieutenant adds 1 multiplier and 10 points per multiplier as opposed to a Strike on a regular-sized enemy, and it's also a lot faster. However, the Lieutenant won't just stand there to let you hit him, so you should Evade if he's about to hit you. Evading/Redirecting toward a Lieutenant's back and Striking him is a common strategy because he cannot reach behind his back (this is true even for Sickle who swipes his weapon in an arc). The equivalent of a Beatdown Finisher on a Lieutenant is called a "Lieutenant Takedown", which adds 1 multiplier and 50 points per multiplier.
 * Another way is to use a Directed Aerial Attack on a Lieutenant. Simply do an Aerial Attack on a regular-sized enemy, then immediately redirect it toward the Lieutenant. This move deals more damage, but is also riskier because you can get hit by surrounding enemies, so it's preferable to use it as quick characters, such as Catwoman. Also beware that a Directed Aerial Attack will prioritize targeting a Lieutenant.
 * Lieutenants are also affected by Batman's Special Combo Bat Swarm, Catwoman's Special Combo Whiplash, and Robin's and Nightwing's Group Attack. These moves only deal minimal damage on individual enemies, but if you have depleted enough of the Lieutenant's health with other ways, it's possible for these moves to deal the finishing blow.
 * Nightwing's Group Electrify, an electricity-based attack like an REC, can also cause a Lieutenant to brandish his weapon around and cause Collateral Damage. Since Special Combo Moves such as Group Electrify give you temporary invincibility, you can perform this move close to him without harm.