No, you do not need cheats to get the rarest Pokemon. The only way to get the rarest Pokemon without cheating is to go to a Nintendo Event, held every few years or so, and download the rarest Pokemon there. Otherwise, you would need cheats to get the rarest Pokemon.
The rarest Pokemon is Dialga
there is no rarest Pokemon you have to train and train and including shinies there is no real rarest Pokemon at all.
You can find the bestest,rarest, Pokemon is to go to www.marriland.com/pokemon
Get the best pokeballs and go search for it.
mew2 is the rarest
Arceus and Deoxys are the rarest Pokemon to date
Pikman or Pokemon The Rarest is mewtwo
The rarest is stantler.
zekrom
By far, they have said Celebi is the hardest/rarest Pokemon to obtain outside of Japan.
i never played Pokemon fire red but the rarest Pokemon IN fire red is obviously mew ... who ever wrote that is an idiot ... the rarest Pokemon is mewtwo ... mew can not be obtained in fire red ... and you get mew two by getting the ruby and Sapphire and then you go to cerlean cave to get mew two after u have completed the E4 and have gotten the ruby and Sapphire ... i hoped i helped