Description
"Defeated the Rakk Hive, the Vault Boss, Sledge, Krom, or Flynt in a co-op game"
Strategy
With at least 1 other player, kill any of the aforementioned bosses. Specific strategies for each boss can be found at their wiki pages.
It is also possible to 'glitch' this achievement by killing a boss and then, without turning the mission in, saving and quitting then opening a new game (split-screen or online) where the character that just defeated the boss is the host.
Trivia
- From the phrase "United we stand, divided we fall."