Best of the Best
As I explained elsewhere, the Best of the Best of the Best (BotB) banner is the reward for completing every challenge category (or Mastery) in the Multiplayer. The individual challenges cover nearly every imaginable facet of the game, from using different characters and weapons, to dealing damage with specific powers, to being a good teammate (measured in rather lackluster way through the number of First Aid medals).
It is not necessary to complete all of them for the BotB. Usually a challenge category consisting of, say, 12 challenges, is declared complete upon finishing 9 or 10. Once you’ve unlocked around 75% of the manifest, this becomes a matter of patience and persistence (or grinding), rather than of skill, but it does serve a greater purpose in making you try out nearly everything the game has to offer and form at least somewhat informed taste.
See, many characters, weapons and powers seem extremely awkward, if not downright useless and unusable, when you first pick them — but by the time you’ve played 10 or 20 games with them out of necessity of completing this challenge or another, you find that they’re not half as bad as you thought. I’m sure I would never have touched half the characters and weapons, if not for the BoTB. And some I really never did touch (Volus Mercenary, Drell Assassin, Katana and Mattock, to name a few) — until I went on a crusade to complete every single challenge, and that was only recently.
The most difficult part for a relative newb (getting the BotB also serves as proof that you’re one no longer), is to finish any three of the four solo challenges: ten solo games on Bronze, five on Silver, two on Gold and/or one on Platinum difficulty. The two Gold solos I did for this challenge with the Krogan Battlemaster and Reegar Carbine vs. Geth (a ridiculously overpowered setup by my current standards), took me one whole hour each (whereas a full-team Gold game usually takes around 20 minutes), and were certainly among the hardest, but also the most exciting and most rewarding games in my entire Multiplayer experience.