True Hero Status is a bar you fill by collecting studs (the game's currency), each being worth a different amount, once you fill up the bar, you get True Hero Status.
In the case of the DLC Levels, you unlock the achievement after you beat a stage with True Hero Status, not just getting it mid-stage
Here's what i like to do:
After a few levels from the main story, you unlock Plastic Man, who is the only character who can unlock red bricks, some red bricks multiply the stud's worth by x2, x4, x6, x8 and x10 respectufully, one more expensive then the last, with x2 Studs costing 1,000,000 studs and x10 costing around 5,000,000 studs. So the strategy is once you unlock Plastic Man and get 1,000,000 studs as you play through the story, go back to the first 5 levels of the story on Free Play Mode, collect the Red Bricks, save and exit and buy the x2 studs red brick, this will give you a lot of money very quickly as you play through the story and will help you fill the True Hero Bars much quicker, so always save money to buy the Stud Multipliers, because chances are that with this strategy, you will have millions of studs without even finishing the story. Good luck!