These Pokémon have more than just collectors' value, though. By
tucking the event Pokémon into the Pokémon Dream World, a new Pokémon
Movie" home, which is based on Eindoak Town, will be unlocked and an
exclusive C-Gear skin of the tucked-in Pokémon is also unlocked upon
completing a game there with Victini.
Tuck in your event Zekrom or Reshiram, you can go to a new "house". On that house, take the Dream Bridge to a new Island of Dreams. Complete the mini-game with Victini and unloc your C-Gear skin.
Then go to the home page, click "Customize" on the bottom right.
Select the skin and wake up your Zekrom or Reshiram.