Transfering heros?

What needs to be done to make a hero transfer over to the next map in a sequence? Is it simple, hard, and how does it work?

On Bnet or single player?

Single Player. custom campaign thing.

"All You Ever Wanted To Know About the Game Cache ++ DLX v.999.77555743"

http://www.wc3campaigns.com/forums/a...ticle&artid=39