Main Mission 36: Prism Tower's Dark Turn

After you reach Rank A, an explosion wakes you up in the middle of the night.

Go to Prism Tower

Use the map to go to Prism Tower, then approach Vinnie and the others.

Battle Urbain/Taunie

When you're ready, talk to Urbain/Taunie to start the battle. Urbain/Taunie of Team MZ has a level 62 Meowstic, a level 63 starter Pokémon that is weak to the starter you chose, a level 63 Manectric, a level 62 Goodra, a level 62 Avalugg, and a level 64 Pokémon that is strong against that starter Pokémon that you chose, which they Mega Evolve. You get 5120 Pokédollars for winning.

Talk to Vinnie when you're ready to proceed. This begins Main Mission 37: Operation Protect Lumiose.