Here is the full list of all 12 Buku Sudoku achievements worth 200 gamerscore. It takes around 6-8 hours to unlock all of the achievements on Xbox 360.
Reach 10,000,000 Buku Score
Complete 200 puzzles.
Complete 25 Multiplayer Games, in either Online or Local Multiplayer game play.
Complete 20 Xbox LIVE Games.
Complete 1 puzzle in Co-op, Team Battle, and Duel in Xbox LIVE mode
Reach 2,500,000 Buku Score.
Complete all the tutorials.
Beat the time limit for 10 puzzles in Timed mode.
Complete a puzzle of each difficulty.
Beat a puzzle in each grid size: 6x6, 8x8, 9x9, and 12x12.
Solve 10 puzzles without any helpers.
Complete a single player 9x9 puzzle in 1 minute and 20 seconds.