Death Track: Resurrection

The Megakiller status is obtained when you kill 2 enemies in 4 seconds, then when you kill a third enemy in the following 6 seconds. There's a challenge about it. To get Megakillers easily, with level 4 weapons, just get behind the pack, and fire everything you have. Getting a damage multiplier really helps, and when you get Killer and Megakiller statuses, you get damage multipliers to chain the enemies and do rampages.