[HELP]Making plataform games enemies

Well,basically,i want to make some baddies in my plataform game:

but i don't how to do some things like:

-Making the bad guy follow a default path

-Making the bad guy spot the main character and pursue him

-making the bad guy knock back a little after getting damage

so if you can answer at least one of the questions i'll be very grateful

(but if you answer all of them it'll be great too <img src="smileys/smiley17.gif" border="0" align="middle" /> )

thanks

You can already find some of the answers to these questions in the how do I FAQ.