Characters: Jean Grey, Cyclops
After the beginning of the mission, approach to the fires - then you will see that Stan Lee is surrounded by the flames. Switch into Jean Grey and take control over his mind, so you can build a device from nearby bricks. When it is done, return to the main character and move violet valve using your telekinetic skills (interaction button). In this way you will extinguish all fires.
Turn right and approach to the violet bricks. Pick them up using telekinesis, then arrange them into the X letter (on the right). When the hidden entrance is open, enter the building.