Last Standing is the original and most widespread WinCon required for a faction to win. It is achieved by one faction when at least one of its players is still alive while no players from other factions are alive. When games include only 1 faction with Group Kill (Baddies) there is usually an equivalent Be in Majority WinCon. In games which include Indy factions, the above WinCons are no longer equivalent, as Last Standing prevents any other faction from gaining a tie-win.
All Last Standing / At least X alive in the end - In rare cases, this WinCon was augmented by the requirement that at least X players (or sometimes the whole faction) need to be alive at the end of the game. However, this harder-to-achieve variation has the potential of leaving a faction without an achievable WinCon during the game, playing without a goal in mind. Hence the practice is (heavily) discouraged for hosts.
Among X Last Standing - An easier variant where only survival till the last X (typically 2 or 3) players is needed in order to win. This WinCon has been adapted for Indy factions which do not have a kill ability, and as such, cannot directly eliminate the other factions and have limited numbers and voting power to eliminate their opposition through lynches. Technically, if the other factions have elimination-based WinCons (such as classical Last Standing or Be in Majority), this WinCon can be fulfilled (if X=3) before those WinCons, awarding a preemptive Indy win in a 1 Baddie vs 1 Goodie vs 1 Indy ending.