"Sonic" games often share basic gameplay, but some have game mechanics that distinguish them from others. For instance, "Knuckles' Chaotix" is similar to previous entries in the series, but introduces a partner system whereby the player is connected to another character via a tether; the tether behaves like a rubber band and must be used to maneuver the characters. "Sonic Unleashed" introduces the Werehog, a beat 'em up gameplay style in which Sonic transforms into a werewolf-like beast and must fight enemies using brute strength. Both the "Sonic Storybook" games feature unique concepts: "Secret Rings" is controlled exclusively using the Wii Remote's motion detection, which "Black Night" incorporates hack and slash gameplay. While some games feature Sonic as the only playable character, others feature multiple, who have alternate movesets and storylines. For instance, in "Sonic & Knuckles", Knuckles goes through the same levels as Sonic, but his story is different, he explores different parts of the levels, and certain areas are more difficult.