Sickle

"I shall slice you into pieces, American."

Sickle, also know as Captain Abramovici, was one of the Abramovici Twins and was the left side of his conjoined brother, Mr. Hammer. Sickle and Mr. Hammer were both Russian.

Before Arkham City Incident
When the twins' mother died during their birth and their father abandoned them to a traveling freak show, the twins grew up and became the headlining act. Joker then sent Harley Quinn to Russia to recruit the twins. After the twins' employer refused, the owner ended up dead and the twins were brought to the Joker.

The Joker then ordered a doctor named Tommy Elliott brought in to perform a separation surgery. After a successful operation, Joker decided to keep one of the twins, while discarding the other. A recovering Sickle was thus thrown outside the Iceberg Lounge. Penguin then ordered aid to be sent to Sickle and planned to use him for his future plans.

Arkham City Incident
Eventually, Sickle became Penguin's one armed lieutenant in his army. He first appeared in The Cyrus Pinkney Institute for Natural History, in the Gladiator Room right after Officer Best was shot by Penguin. Sickle held Officer Jon Forrester by the neck while Penguin addressed Batman and started the "initiation." Sickle, Penguin, and the other henchmen left Batman to die.

Batman survived and followed Penguin. Sickle had separated from his leader at that stage. He appeared once more in the Museum War Room. As Batman attempts to rescue Mr. Freeze, Sickle bursts through a wall with a number of henchmen. They fought with Batman, who once again triumphed, and knocked them all unconscious.

Sickle was last seen reconciling with his brother, Mr. Hammer, in the Assembly Line at the Steel Mill. The twins' considered getting stitched together so that they could be together again. If you did an Environmental Analysis on them, you solved the riddle: "Once assembled, do these two become one again?"

After Arkham City Incident
It could be assumed that Sickle and Mr. Hammer were taken to temporary holding cells when the GCPD invaded the mega facility.

Before Arkham Knight Incident
Hired by the Penguin, Sickle and his brother were tasked with finding Scarecrow. After several days, Sickle tracked down a lead that led the pair to Crane's Lair. The twins' were captured and tortured before they were set free, stitched back together against their will, and Sickle was unable to regain consciousness with straw stuffed in his mouth.

Quotes

 * "Look at you! How can you beat me?!"
 * "You look so strong. You're not so strong. I kill you with one hand."
 * "Why won't you die?"
 * "I shall kill you!"

Trivia

 * Sickle had "✰" tattoo, which shows his Russian origins. Also, his brother, Mr. Hammer, wielded a large sledgehammer. Sickle himself wielded a large sickle. Hammer + Sickle = ☭. Symbolizing the socialist republic of the Soviet Union.
 * Sickle was seen in The Joker's Carnival Challenge Map, along with Mister Hammer.
 * It took 50 hits to take Sickle down. If you did so uninterrupted, you got the 50X achievement by fighting him alone.
 * Sickle claimed to be much stronger than his brother.
 * The fact that his brother wielded a hammer, and he a sickle, was a reference to the Soviet Flag, which has a hammer and a sickle crossing it. That was a reference to how the two were Russian.
 * In the Arkham Knight prequel comics, it's revealed that Sickle had a stage name: Captain Sickle. Just like how his brother Hammer had the stage name: Mister Hammer.