Enemy AI needed for fighting games

I want to make a fighting game 2D like Mortal Kombat with kicks jumps punches and some special moves. I can handle the user part.
But I didn’t know how to script the AI of enemy to kick, block or what to do. I have searched the net for this enemy ai but…zero.

The enemy must respond to player in some what and all the animations for player are the same for enemy.

Also I want to know how to implement the difficulty factor as the level progresses…

Thanks in advance…