*THIS MAY REQUIRE AN INTERNET CONNECTION* Bro Buffs are just the boosts you get from having "bros," or friends, that play the game. The more bros you have, the better the boosts you get. It is advised that you acquire the allowed maximum of 10 bros in order to decrease the overall completion time, as almost every aspect of the game is boosted when you have bros. See this forum if you need more bros.
**GLITCH** Some folks are having trouble getting their friends with the game to actually show-up as bros, making this achievement unattainable. The problem seems to be specific to certain countries (Norway, Nederlands...), but may be a small issue everywhere. It could possible be related to individual phone models, but that does seem unlikely as it has been reported on the Titan and Lumia 800. "The Bro-Up" achievement is still obtainable however.