Sickle

Sickle, also referred as Captain Abramovici, is The Penguin's one armed lieutenant in his army. He was mentioned to be with his conjoined twin, Mister Hammer, performing at a Russian circus. They got into an argument and split up, joining separate factions in Arkham City.

Batman: Arkham City
Sickle first appears in the Cyrus Pinkney Institute for Natural History, in the Gladiator Room right after Officer Best is shot by the Penguin. Sickle holds Officer Forrester by the neck while Penguin addresses Batman and starts the "initiation". Sickle, Penguin and the other henchmen leave Batman to die.

Batman survives, and follows Penguin. Sickle has separated from his leader at this stage. He appears once more in the War Room. As Batman attempts to rescue Mr. Freeze, Sickle bursts through a wall with a number of henchmen, they fight with Batman, who once again triumphs, knocking them all unconscious.

Sickle is last seen reconciling with his brother, Mister Hammer, and talking to him in the Steel Mill. They consider getting stitched together so they can be together again.

Trivia

 * Sickle has "✰" tatoo, showing that he has origins from Russia. Also his brother, Mister Hammer wields a large sledgehammer. Sickle himself wields a large sickle. Hammer + Sickle = ☭.
 * Sickle is obviously left-handed, due to the cause of being a conjoined twin with Mister Hammer.
 * Sickle is seen in the "Joker's Carnival" challenge map, along with Mister Hammer.
 * It takes 50 hits to take him down. If you do so uninterrupted you can get the 50X achievement by fighting him alone.