A film or series "in which beloved aging stars reprise classic roles and pass the torch to younger successors." Matt Singer coined this word in an article about Star Wars: The Force Awakens, also mentioning Indiana Jones and the Kingdom of the Crystal Skull.
Pulling a LegacyFall12 means you wallbang at least two different people each round of Rainbow Six Siege, usually with headshots. Ultimately making people whine, cry, and call you a hacker.
When your mediocre-at-best friend starts screaming that he pulled a legacy fall, you know he got at least two wallbang headshots that round of Rainbow Six Siege. Because LegacyFall12 is a wallbanging god.