Just as the Hulk is about to smash Black Widow, Thor arrives. Follow the on-screen prompts to attack Hulk. However, Hulk eventually grabs Thor and throws him. While flying backwards, maneuver left and right to avoid obstacles and collect some studs.
Thor and Hulk end up in a large room. Throw Thor’s hammer at Hulk and then while Hulk is trying to pick up the hammer, jump onto his back. Make him run into one of the cracked LEGO pillars near the back of the room. Throw the hammer at Hulk again and make him run into the second pillar as well.
Now fly up and charge the two generators with Thor’s lightning. This opens a control panel in between the generators. Fly over to it and press the button to send electricity down to the metal floor where Hulk is standing.