This achievement involves the online 'Grade' leaderboards. Your leaderboard Grade depends upon how many Ranking Points you have.
To get this achievement, you need to reach Grade TM, which means you need to get 14000 Ranking Points.
The Grades are split up into the following Ranking Point ranges:
Grade | Ranking Points
----------------------
TM = 14000-15000 RP (15000 is the maximum RP you can have.)
S+ = 12000-13999 RP
S = 10000-11999 RP
S- = 8000-9999 RP
A+ = 7000-7999 RP
A = 6000-6999 RP
A- = 5000-5999 RP
B+ = 4000-4999 RP
B = 3000-3999 RP
B- = 2000-2999 RP
C+ = 1200-1999 RP
C = 600-1199 RP
C- = 0-599 RP (0 is the minimum RP you can have.)
You start with 0 RP. You increase your multiplayer Tetris Grade by winning versus games across Xbox Live. You decrease your RP by losing versus games across Xbox Live. The way Ranking Points (RP) are awarded is very simple:
0-Grade difference: Winner = +200 RP. Loser = -200 RP.
1-Grade difference: Winner = +150 RP. Loser = -150 RP.
2-Grade difference: Winner = +100 RP. Loser = -100 RP.
3-Grade difference: Winner = +50 RP. Loser = -50 RP.
4-Grade difference (or more): Winner = +10 RP. Loser = -10 RP.
Examples:
Your Rank = A-
Opponent Rank= C+ (or lower)
If you win, you gain 10 ranking points. If you lose, you lose 10 ranking points.
Your Rank = A-
Opponent Rank= B-
If you win, you gain 50 ranking points. If you lose, you lose 50 ranking points.
Your Rank = A-
Opponent Rank= B
If you win, you gain 100 ranking points. If you lose, you lose 100 ranking points.
Your Rank = A-
Opponent Rank= B+
If you win, you gain 150 ranking points. If you lose, you lose 150 ranking points.
Your Rank = A-
Opponent Rank= A-
If you win, you gain 200 ranking points. If you lose, you lose 200 ranking points.
Your Rank = A-
Opponent Rank= A
If you win, you gain 150 ranking points. If you lose, you lose 150 ranking points.
Your Rank = A-
Opponent Rank= A+
If you win, you gain 100 ranking points. If you lose, you lose 100 ranking points.
Your Rank = A-
Opponent Rank= S-
If you win, you gain 50 ranking points. If you lose, you lose 50 ranking points.
Your Rank = A-
Opponent Rank= S (or higher)
If you win, you gain 10 ranking points. If you lose, you lose 10 ranking points.
As you can see, even if you beat someone ranked many grades above you, you'll only get 10 ranking points. This was intentionally done by the developers, so that people would play with people around their own Grade, so that the skill levels are fair. However, they wanted it so that if a lower-Grade player wanted to play a higher-Grade player, the higher-Grade player would have the incentive to play, because they wouldn't lose an incredible amount of RP if they lost.
After you achieve this grade, you have earnt the highest Grade on the Tetris Grandmaster ACE leaderboards, and are now graded as a TETRIS MASTER!
Congratulations!