Right before the boss fight of episode 7 “City of Doom”, you will find yourself on a rooftop with Doombots shooting you from the top platforms and three grey circular vents. During this time, regular Doombots will land on the platform and start attacking the vents. You need to prevent them from destroying a single vent. They all must still be standing when the attack is over. I like to use Spider-man here. You can stand at one of the vents and then press to shoot a web and yank the enemies to you. Ignore the snipers until the rest of the Doombots stop appearing. If you do lose a vent, you can pause the game, select “restart checkpoint”, and try again.