Technically, if you have nothing other than Sonic the Hedgehog 2 on Sega Genesis, you won’t be able to play as Knuckles the Echidna. You had to connect that cartridge with the special Sonic & Knuckles cartridge.
Which allowed you to play as Knuckles for the whole entire game.
So his gliding and climbing powers were at your full disposal.
Which was pretty cool.
This was one of the things that blew my mind as a child. I was always disappointed that it didn’t work for the first game.