i am going to be making a final fantasy bros game by swaping out the mario and baddie sprites with sprites from final fantasy 1 and mabye even from 2 and 3. I was searching around and came across this website:

http://www.nesplayer.com/database/info/emulation/doc/romdoc.html

it sais to use tile layer and swap them out but i am having trouble because some of the mario sprites and mirrored and it can't be like that for the final fantasy fighter.

please tell me the best way that i can do this: to change sprites in a game.

I don't think that's what he means. I think he means that, when standing still, the right half of Mario's body uses the same tile graphics as the left half, just flipped in memory.

http://www.freewebs.com/insectduel/AdvSMB1.htm
this is pretty cool but i need help where and how to locate the grid spots where i would replace the sprites. If you know anyother website that can help general rom hacking please let me know. thanks.