For those of you who don't feel like watching a video, here's a summary:
- Getting 600 kills
- Completing a map (any difficulty except Casual)
- Completing a map on Hardcore
- Completing a map with at least one relic (non-casual)
- Prestige (+1 each prestige)
- Obtain the following ranks (no-prestige): 2, 6, 11, 21 (+1 each)
- Bonus Pool (barrier hives)
- Assist at least ONE other player in getting their first (non-casual) escape/victory on a map.
Hope this is helpful for those of you who don't know about this. These are the official proven ways. All of them. No theory, plain facts!