Unable to go get my gym 8th badge in Black2, help? Did I miss something?

Question

I have defeated the 7th gym leader received badge and beat rival. But cannot go thur marine tube. Not sure if I had miss something.

Comments

Thank You Both.
I went back to Opelucid City. I missed the Shadow Triad battle. Once I battle him everything fell into place.

Again Thank you for your help.

Answer 1

Well, after you beat Drayden and get your 7th badge he should tell you to go visit him in his house. You must do this :L
After you go visit him, he goes onto something about Zekrom/Reshiram, and after that happens Team Plasma will appear and freeze up everything. You'll need to go battle Zinzolin (One of the sages) and a member of the Shadow Triad before this part is completed. Cheren will then come and tell you that Team Plasma's ship[ was spotted near Humilai - the site of the last gym
After this go back to Undella town and you'll be able to get there.

Source: http://www.marriland.com/black2_white2/walkthrough/basic-badge/4184-opelucid-city?cookieTest=1

Answer 2

After you beat Drayden you go to his house and he will tell you about Reshiram and Zekrom. Then, Team Plasma freezes Opelucid City and you have to defeat a bunch of grunts. Next, you have to go to the Opelucid Gym and defeat Zinzolin who stole the DNA splicers. Last, you must beat a member of the Shadow Triad next to the east gate. The Marine Tube should then be open to go through.e

Also, when you get to Humilau City, Marlon, the Gym Leader, will not be there. You will have to go to the northern part of the city, when you're just about to enter the first house, he will come up out of the water and return to the Gym.

Hope I helped! :)