Look Out Below! Achievement.
You'll need to at least reach the Tomb of Eilram to unlock Forcepush (RT) to unlock this achievement. Use either Forcepush (RT) or Forcepull (LT) to knock 25 enemies off cliffs or catwalks to their death. It doesn't have to be 25 with either LT or RT, you unlock Forcepush (RT) much earlier in the game and I popped mine using Forcepull (LT). Take advantage when coming into new areas and just push Stormtroopers off cliffs for easy kills before they aggro. Good Luck!