I have a Pokemon guide that says if Victini is brought to liberty island "something unexpected might happen".
If a Victini is brought to Liberty Garden and into Victini's room, Victini will request to come out of its Poké Ball. If the player accepts, Victini will come out, reminisce about the past and examine its old room. Afterwards, Victini returns to its Poké Ball.
Hope I helped! :) Source
Nothing really big happens. Once you go to liberty garden, enter the building and go to the back room. All that happens there is that the victini will come out of the pokeball and look around the room. Then return to its pokeball.
This video will show you it: - https://www.youtube.com/watch?v=pweJ_S_d1B4