To get Manaphy you must have the Action Replay. If you need the code search Google for "pokemon pearl - how do you get manaphy?" That should do it.

its a thingy.

you get pokemon ranger and do the egg mishon then borrow another nds and send the egg to pokemone dimend or pearl and then walk/run for 6500 steps.

then go to poke mart. there should be green man there

finish pok'emon ranger and tranfer manaphy egg