After getting the nationaldex, go to one island and talk to celio. He will tell you to find the ruby and sapphire gem and give you the rainbow pass which give access to the 4, 5, 6 and 7 islands. If he does not give the pass, first find the ruby gem in Mt. Ember and give it to him. Then, he will surely give you the pass.
After getting the national pokedex get the ruby and give it to celio. he will give you the rainbow pass for islands 4-7.
You must beat the elite 4!Then you can go to 4,5,6,and 7.
you have to beat the elite four and then go talk to pro. oak and i think he gives you the pass.
its actually the 8th gym so you need 7 badges and then it will unlock
You have to find the key in the abandoned mansion.
You have to beat the elite 4 and get the National Dex.
Defeat team rocket in the game corner, Pokemon tower and silph co then receive 7 badges.
you have to complete the last castle but you have to do it all in one to go back and unlock them.
with the tri-pass you unlock islands 1-3. with the rainbow pass you unlock islands 4-7
you beat the world 2 final boss as mini Mario and you will unlock world 4. Do the same thing in world 5 to get world 7
All i know is that the mini mushrooms are in world 2 boss castle(to unlock world4) and world 5 boss castle(to unlock world 7) you have to beat the worlds 2 &7 boss when your mini Mario, in order to unlock worlds 4 & 7, it will be a little difficult beating the bosses when your mini Mario but it's worth it
It's seavault canyon and it's on 1 of the 7 islands after you beat the elite four when you unlock the islands check your townmap to see which island it's on