Justin Yu, known online as Fractal161, is an American classic Tetris player from Dallas, Texas. He is best known for his victory in the 2023 Classic Tetris World Championship (CTWC), for becoming the second person to "beat" the game, and first to achieve its earliest possible game crash on January 3, 2024.

Beginning to play Tetris around 2016, Yu entered the competitive scene around 2019, and was one of the first players to fully adopt a new and faster playing style called "rolling". Through repeated practice and by studying the game's programming assembly, Yu finished as the runner-up in the 2022 CTWC and won the 2023 CTWC while also a Junior at the Massachusetts Institute of Technology (MIT). After winning the CTWC, Yu focused on becoming the first person to "beat" Tetris. Although he became the first to reach the late-game glitched color levels before a game crash, Yu was beat to his goal by fellow competitive Tetris player Willis Gibson ("Blue Scuti") on December 21, 2023. A few weeks later, Yu became the first player achieve the earliest possible game crash. Yu has stated he wants to one day run Tetris websites and tournaments when he leaves the competitive scene.

Yu is from Dallas, Texas. In high school, Yu participated in a number of math competitions, helping him to get accepted into the Massachusetts Institute of Technology (MIT) with a major in computer science and engineering. As an alumnus of the class of 2025, Yu has pursued another major in mathematics, with a minor in music technology. Yu also plays the cello in the MIT Video Game Orchestra, an orchestra at the school which performs covers of classic video game music. Yu has stated he places the Video Game Orchestra and other school commitments above practicing Tetris.

Yu began to play the original NES Tetris around 2016, becoming interested after watching videos of the game on YouTube, but never playing for more than an hour at a time. He began to pursue the game more competitively around 2019, playing in three to four hour sessions, where he often practiced to optimize his strategy. To get a better understanding of the game, Yu began to experiment in programming assembly and ROM hacking, which helped him to become the first person to reach Tetris's late-game glitched color levels, and in his major at MIT. In the 2022 CTWC, Yu finished in second after losing to Eric Tolt ("EricICX") in the finals. As a Junior in college, Yu again competed in the CTWC from October 13 to 15, 2023, where he beat fellow competitor Eve Commandeur ("Sidnev") to place first, winning over US$3,000.

After the 2023 CTWC, Yu announced his intentions to try to "beat the game" by reaching its killscreen, a point late in the game where the code glitches, resulting in a game crash due to hardware limitations within the NES. Fellow competitive Tetris player and YouTuber Willis Gibson ("Blue Scuti") became inspired by this goal and competed against Yu for over two months to become the first to the achievement. Yu particularly struggled with a level nicknamed "dusk", which he described as "so incredibly dark that I felt as if I'd been blinded for a split second." While fixing the issue by purchasing a universal remote which increased his TV's brightness, Yu learned Gibson was close to crashing the game, and watched his livestream where Gibson ultimately "beat the game" on December 21, 2023. Yu celebrated the achievement with Gibson, exclaiming "He did it, he did it!" on his own livestream. Yu continued to work towards the goal, and on another livestream on January 3, 2024, he beat the game, becoming the second person to do so after Gibson and first person to achieve the earliest possible game crash on level 155, two levels quicker than on Gibson's run. After the large amount of media coverage that came from beating the game, Yu argued he did not want the message to read as "We've finished up!" to potential new players, when other achievements such as the "perfect Tetris game" consisting of only the highest scoring line-clears called "tetrises", and "rebirth", playing the same so long it restarts at level one, had both yet to be done.

In early 2024, Yu hosted his own Tetris event at MIT, which only through word of mouth had between fifty to sixty attendees. From June 8–9, Yu competed in the 2024 CTWC, where he was eliminated in the Round of 16 by Tristan Kwai ("Tristop"), who went on to win third place. Yu has stated his future goal is to one day help run Tetris websites and tournaments as opposed to competing in them, believing the large effort needed to run them often goes unnoticed.

Shortly after Yu began to play competitively, he was among the first to change their playing style to "rolling", a technique which involves rolling the back of the controller with all five fingers to position the game pieces more quickly. This became crucial to beating later levels of the game and to staying competitive in modern tournaments. In a February 2024 interview with the newspaper The Tech, Yu stated his strategy revolved less around making "the board look as nice as possible", and trying to focus on completing tetrises.

Below is a table of the Tetris tournaments Yu participated in and their outcome. It should be noted the table is likely incomplete, as results on the CTM website prior to February 2022 only list the name of a competitor if they won or were the runner-up, not including the names of those who competed otherwise.

Year	Tournament	Score	Finishing place	Ref.
2020	CTM April Challengers Circuit	2–3	2nd
	CTM August Futures Circuit	3–1	1st
2021	CTM April Challengers Circuit	2–2	2nd
	CTM June Challengers Circuit	3–0	1st
	CTM August Masters Event	4–0
	Classic Tetris World Championship	3–2	14th
2022	CTM March Masters Event	0–1	Contender
	CTM April Masters Event	3–2	1st
	CTM May Masters Event	2–1	Contender
	CTM June Masters Event	2–1
	CTM July Masters Event	4–0	1st
	CTM August Masters Event	4–0
	CTM September Masters Event	2–1	Contender
	Classic Tetris World Championship	4–1	2nd
	CTM November Masters Event	2–1	Contender
	CTM December Masters Event	1–1
2023	CTM January Masters Event	0–1
	CTM Mega Masters	2–1
	CTM Lone Star Championship	0–1
	CTM PAL June Tier 1	6–1	2nd
	CTM August Masters Event	1–1	Contender
	CTM September Masters Event	1–1
	Classic Tetris World Championship	5–0	1st
	CTM November Masters Event	3–1	2nd
	CTM December Masters Event	2–1	Contender
2024	CTM January Masters Event	4–0	1st
	CTM February Masters Event	4–0
	CTM Mega Masters	6–0
	CTM April Masters Event	1–1	Contender
	CTM May Masters Event	1–1
	Classic Tetris World Championship	1–1
	CTM July DAS Masters Event	2–1
	CTM August DAS Masters Event	0–1
	The Jonas Cup	5–0	1st