Scratch

You mean a computer character? This is very hard to make...

If you want a multiplayer one for two players, just make two sprites which look different and have different controls.

dingdong wrote:

wait I don't understand do you co-op or do you want a versus? and do you want it to scroll?

He said nothing about scrolling...

Well, this is a project that you can't just say "how". You need to break it into parts, like a title screen. "How do I make it so when the button is clicked, the game starts?"
I would say "Use the broadcast system. Broadcast Single Player for one and Multi player for the other"
Then you ask another question, maybe (example) "How do I make him move?"
I would say "Use the forever if block and change your X by a number since then you don't need to worry about your costumes pointing in the right direction."

See?