This sounds like Invasion Slayer, but with spawns being hot-dropped, and an assault twist after a set number of kills. -blam!-, if you could just change some scripts for Invasion, it could be put in there. Instead of capturing A or B, it could be kill 50 Spartans (for Elites), then kill 50 more, then get a bomb from one side of the map to an objective marker (the Spartan base).