Here is the full list of all 12 Galaga Legions achievements worth 200 gamerscore.
Cleared Area 1!
Cleared Area 2!
Cleared Area 3!
Cleared Area 4!
Cleared Area 5!
Cleared all areas in Championship mode!
Cleared Area 2 in Adventure mode!
Cleared Area 3 in Adventure mode!
Cleared Area 4 in Adventure mode!
Cleared all areas in Adventure mode!
Area cleared without deploying any satellites!
Area cleared without losing a single fighter!