Since Sonic & Knuckles and Sonic the Hedgehog 3 were initially developed as one game, their gameplay is similar: both are 2D side-scrolling platformers with similar level design, graphics, and game mechanics. However, in Sonic & Knuckles, unlike in Sonic 3, the player chooses either Sonic or Knuckles at the title screen,[4] Miles "Tails" Prower is not available to select, and the player cannot control two characters together. There is also no multiplayer mode or save feature.[5]
The player character moves through six levels, each divided into two acts.[6] The first act of each level ends with a miniboss fight with one of Dr. Robotnik's robots,[7] while the second ends with a regular boss fight with Robotnik (or EggRobo in Knuckles's campaign).[8] Sonic and Knuckles traverse levels differently; Sonic can jump higher and has access to unique shield abilities, whereas Knuckles can glide and climb most walls. The levels also include cutscenes that differ based on the character selected, as Sonic and Knuckles are opponents for most of the game.[4]