Okay first of all you have to get the pokeblock case from the lilycove city contest halls and he should let you in.
Shedninja it is part bug and part ghost, it is the only Pokemon with the ability wander guard
there is no saffron city in Pokemon emerald, and there is no "Pokemon bluesea" but you can catch both Groudon and Kyrouge in emerald... blue sea is a fake created by some guy who needed some money.
http://www.kidzworld.com/article/5900-pokemon-emerald-game-cheats-rare-and-shiny-pokemon
no you need game shark
The Pokemon that can inherit No Guard are Machop, Machoke, and Machamp.
First, you have to defeat the Aqua team at Mount Prye, then you have to defeat the Magma team at their hideout near Lavaridge. Then, the guard will be gone.
You must 1st beat the game by taking on the Elite Four. Then if you get the ruby and Sapphire so that you can trade with Hoen region (Pokemon Emerald,Saphire,Ruby) then go talk to the guard and you will be able to get in. In cerulean cave you can find Mewtwo if you go the write way and be sure to bring escape ropes.
No Pokemon with wonder guard is an abilty that prevents non super effective moves to effect your Pokemon
machoke
It is impossible to teach wonder guard to a Pokemon, even for action replay because wonder guard is a ability, which cannot be changed. Only shedninja has the ability. Whoever says that a Pokemon other than shedninja has wonder guard, they are lying.
Shedinja
So far only Shedinja has the ability Wonder Guard.