If you aren't able to register for the Pyrite colosseum you need to battle every trainer in Pyrite and then go to Duking's house(rusty with a G type leter on it) walk over to the right side of the bookshelf the boy is in front of and it will say "there is a button on the side,push it?" push yes and go in talk to the girls and come out a man will be talking to duking,something will happen at the windmill and a gear will be gone,the gear is at the construction site on the map,go there and walk up,right an and you will see a shiney circle like thing, take it back to the windmill and you may now enter at the colosseum.