Mesprit & Cresselia (legendary)
the hardest Pokemon to find is regigigas you can only get him after finding all the other Pokemon and you can find him in the hippodow temple
latias
feebas
in the dungeon
Charmander, Squirtle, Bulbasaur. You are always given them, you don't find them!
Shiny Pokemon are the hardest to find most likely you will not find one just look in the lake of rage to incresse your canches
Using action replay its arceus (it's the strongest Pokemon in the game!) which you need to get azure flute then go to spear pillar. The other hardest would be mespirit and cresseliar because you have to chase them around the map.
Magikarp
A fleeing legendary pokemon
If you are looking for a shiny pokemon, look hard Because they are the hardest type of pokemon to find. In pokemon games like pokemon pearl, Diamond and stuff, You have 1 in 1800 chance of finding one. I have found one though.
darkrai and arcus
You find old rod at dewford town You find Good rod at route 118 You find Super rod At Mossdeep town in a building. (Hardest to find)