Each of the 3 characters from this pack have only 1 Heroic Feat and they are all the same: Defeat 50 enemies with their heroic attack. Go into Challenge mode, select whichever of the 3 you want to start with and pick whatever survival challenge you like. I used the first one with the Skrulls and you can get 10 to 20 kills per round depending on how long you can last. Basically fill your meter, get in a group of enemies and pull to unleash your heroic attack. Repeat as needed. Once you have the first character's achievement, back out to the character select screen with , select the next person and start over again. It takes maybe 10 minutes per character so you are looking at 30 minutes for the full 250.