You need 75,000 studs to achieve True Believer status in this level. It is recommended that you have bought and activated the Studs x2 pink brick as it would be very difficult to obtain this goal without it. This brick is already unlocked and located in Gwenpool’s room in the Avengers Mansion and costs 800,000 studs.
Once you’ve purchased it, enable it in the pause menu and then start the level. Play through the level and once you achieve ‘True Believer’, if you are playing Story Mode, complete the level to unlock this. If you are playing it in Free Play and have fulfilled all other achievement requirements for this playthrough, you can quit out and press save and exit to get the achievement.