2.MISSIGNO and M
There are two ways to get these pokemon.First one is to go to Cinnabar Island and trade with one of the guys in the building. Then you go to the right side of the island and surf up and down(half in the water and half on the ground). Tada!!!!!!! Now either Missigno or M will come out.
Second way is to go to Viridian City and talk to the guy who shows you how to catch a weedle(make sure that you say no!!)and then fly to Cinnabar Island and surf up and down at the right side of the island(half in the water and half on the ground).
If you want to get Kangaskhan easy then you must have M. If you have M then use a rare candy on him. The gameboy will say 'What M is evoving!!' and then it will evolve into Kangaskhan(it is one of the hardest pokemon to get in the game!!!).