Classic Tetris World Championship

Qualifying takes place on a fixed number of NES stations. Entrants play "Type A" Tetris, starting on level 9 or higher, and are seeded based on their final score. Once an entrant's game ends for any reason, his/her score must be recorded by a tournament scorekeeper in order to be valid. Entrants may make as many qualifying attempts as they wish, but must return to the back of the waiting line for each one. Entrants may also pay a fee to rent a station for one hour, which allows unlimited qualifying attempts.

The top 32 scorers are seeded into a tournament bracket for the Main Event. In 2018, 40 players were allowed to qualify, with a "Round Zero" play-off held for the qualifiers seeded 25th through 40th to reduce the field to 32.[4] In 2019, 48 players qualified with Seeds 17 thru 48 competing in "Round Zero" for the remaining spots in the Top 32. In the event of multiple players maxing out (scoring 999,999 or higher), their second highest score is recorded to determine their seeding. This was especially utilized in 2018, when seven players maxed out, four of whom (Koji "Koryan" Nishio, Tomohiro "Green Tea" Tatejima, Jonas Neubauer and Harry Hong) maxed out twice. Thus, the officials needed their third highest scores just to determine the 1st to 4th seeding.[5]

A special cartridge given to supporters of the event in 2013.

The Main Event is a single-elimination tournament consisting of five rounds of head-to-head matches, with seeds from opposite ends of the rankings pitted against each other in the first round (i.e. #1 vs. #32, #2 vs. #31, etc.). Matches are played with specially modified cartridges that can display seven-figure scores and give both players the same sequence of randomly determined blocks. Prior to the 2016 tournament, the Main Event was played using unmodified cartridges.

Both players begin to play "Type A" Tetris at the same time on separate systems, and the game continues until one of the following occurs:[6]

• Trailing player "tops-out," or allows the blocks to reach the top of the screen (leader wins)
• Leader tops-out; trailing player fails to match that score before topping-out (leader wins)
• Leader tops-out; trailing player passes that score (trailing player wins)

During the first round, the higher-seeded player in a match chooses whether the first game will start at level 15 or 18. The lower seed chooses for the second game, and the higher seed for the third (if necessary). Starting with the second round, all games begin at level 18.

The inaugural edition of CTWC had the flavor of an invitational tournament due to its original concept;[7] five spots were automatically filled with the world record holders Jonas Neubauer, Harry Hong (by achieving the max-out, or 999,999 points), Ben Mullen, and Jesse Kelkar (for records of most/second most lines cleared: 296 and 291, respectively), and the 1990 Nintendo World Championships champion Thor Aackerlund. Three spots were remaining for qualifiers: top 3 players in the "Type B" games (with Level 18 and Height 0) in a certain period could join the semifinal.

The 8-player semifinal consisted of three rounds of "Type A" games to decide two finalists: The first was for most lines, and the last two were for most points. Calculated by the percentages of lines or scores compared to the best player of each round, the top two players advance to the final. The final was the best of three head-to-head matches by using "Type A" games.

In the qualifying, top 8 scorers of "Type B" games advanced to the main tournament. An additional 100,000 points were awarded for completing Level 19.[8]

The main tournament was a single-elimination tournament consisting of three rounds, and all matches were the best of three.

As the tournament moved to the Portland Retro Gaming Expo, the rules were renewed and established as the current rules:

• The qualifying uses "Type A" game and the top 32 players are seeded to the main tournament bracket. ("Type B" games are no longer used)
• The main event is a single-elimination tournament with four rounds and a final. Matches in the rounds are played best of three (first to two games) while the final is played best of five (first to three).
• The standings between players reached the same round are determined by 1) games won in the losing match, and 2) combined scores of the two games lost in the losing round.[9]

A slight change was applied in determining the rankings: if players are tied for rounds advanced and games won in a losing match, the sum of two games in the losing match plus qualification score was used. However, this rule was used only in 2015 and 2016.[9]

From 2016, the contenders play with specially modified cartridges during the main tournament. The modified cartridge can count the score in 7 digits and enables each player to receive the same order of pieces, in order to avoid the inequity of I-piece supplies and the periods of I-piece droughts. The referee rolls two 10-sided dice before each game to determine a random seed (and the random seeds in the cartridge are changed every year).

Qualifying games are still played with the original unmodified cartridges.

The number of players for the main tournament draw was expanded from 32 to 40, with a "Round Zero" play-off introduced for qualifiers ranked #25 to #40. The winner of each "Round Zero" match faced one of the top 8 seeds in the first round proper (winner of #25/#40 vs. #8, #26/#39 vs. #7, etc.)[10]

The number of players for the main tournament draw was expanded from 40 to 48, with a "Round Zero" play-off for qualifiers ranked #17 to #48. The winner of each "Round Zero" match faced one of the top 16 seeds in the first round proper (winner of #17/#48 vs. #16, #18/#47 vs. #15, etc.) [11]

Matches in rounds 0-2 are played best of three while rounds 3-5 are played best of five.

Due to the COVID-19 pandemic, the event was held online with a different set of rules from the in-person tournaments.[12]

Qualifying

• Players have 2 hours to make unlimited qualifying attempts, with the Top 64 being seeded for the Double-Elimination tournament.

Double-Elimination Playoffs (Top 64)

• The Top 64 are distributed among eight separate 8-seeded Double-Elimination Brackets.
• All matches are a Best of Five, with all games starting at Level 18.
• Players do NOT get the same order of pieces, as they use the original unmodified cartridges.
• The winner of each bracket advances to the Top 8.

Single-Elimination Playoffs (Top 8)

• The Top 8 are reseeded based on their Top 64 performance.
• All matches are a Best of Five, with all games starting at Level 18.
• Players get the same order of pieces, as they use the specially modified cartridges.

• First level 30 in qualifying round of CTWC: Joseph Saelee, 2018[14]
• First level 31 in qualifying round of CTWC: Joseph Saelee, 2019[15]
• First max-out in CTWC tournament: Joseph Saelee, 2019[16]
• First double max-out in CTWC tournament: Joseph Saelee and Greentea, 2019[17]
• First double 1.1 in CTWC tournament: dogplayingtetris and Koryan, 2020

There is a once-a-month online tournament called Classic Tetris Monthly (CTM) that was previously hosted on the same Twitch channel as the CTWC, but now is hosted on MonthlyTetris. Competitors routinely compete from around the world in CTM, which is streamed remotely and thus allows for great flexibility on the part of the competitors. CTM is overseen and commentated chiefly by Keith "vandweller" Didion, who took over for Jessica "fridaywitch" Starr, the tournament's founder, in the Summer of 2018. Starr premiered the tournament on December 3, 2017 on her personal Twitch channel, with 16 participants that had qualified in the few weeks leading up to the event. Harry Hong, the 2014 CTWC champion, was the tournament's first victor. Didion opened a Twitch account dedicated to CTM, called MonthlyTetris, shortly after he began hosting.

Since 2015, a Classic Tetris European Championship has been played annually in Copenhagen. The tournament follows a similar structure, but is played on the PAL version of NES Tetris rather than the NTSC version. Due to the difference in framerates, the two versions of the game (both of which are designed for the NES) are balanced differently; pieces do not fall at identical speeds on the same level between the two versions. In addition, Delay Auto Shift (DAS) is faster in PAL compared to NTSC. At higher level play, this leads to significant differences in strategy and outcome. In particular, players who employ DAS as their primary strategy are able to play at the highest level.