At 1:01:05 Arkin lets Paz break his arm, then when he fights the collector starting at 1:05, he uses both arms to grab, punch and throw the collector.
(at around 14 mins) When Arkin escapes the party by jumping through a window he is barefoot and bloody. However, while falling from the window, landing on the car, and walking down the street he is wearing blue shoes. Soon after, at the hospital, he is barefoot again.
Elena's bra/undershirt strap disappears and reappears multiple times throughout the film.
When The Collector's dogs attack Arkin and the others, the tattoo on Arkin's right shoulder is missing when he is bitten by the dog.
When Lisa comes to find Arkin in the hospital, there is no mention of the threat hanging over Lisa from those to whom she owed money. Besides, when Arkin tells Lisa to flee, he's not talking about their daughter, Cindy. After all, the end of the first film let it be understood that by not being able to arrive at the rendezvous, he had thus caused their misfortune.
(at around 14 mins) When Arkin breaks through the window to escape The Collector at the club he lands on a parked car. The windows of the car blow out before he makes contact with the roof.