マイティー is a Japanese Youtuber. He posts gaming commentaries mainly of the Dragon Quest series using AquesTalk. He broke some world records and claimed he used an actual console. However, other players noticed emulator-specific behavior in his videos. He lied about what he used to play the games.
Then, how could this be a problem? His challenges were how fast he could beat a boss, how low level he could beat a boss at, etc. The Dragon Quest series is a classical RPG that adopts turn-based combat. Character stats, the action you take, and RNG (Random Number Generators) determine evasion, critical hit, the amount of damage, and so forth. Therefore, one of the key factors is luck — or the number of trials (Another important factor is strategy, but I do not discuss it here because he did not develop a new one). You can easily break actual console records with emulator functions such as savestate, fast forward, RAM watch, cheats, and so forth, and there is no way to prove that you do not use these functions when you play the games with an emulator. Therefore, actual console records and emulator records need to be considered separately. That is why his lie caused a problem.
In addition, considering how often he posts videos and how rare what happens in his videos is, it is almost certain he used emulator-specific features. He tried to make excuses about this, but his explanation was incoherent. Although using an emulator is not illegal or taboo in Japan, Japanese Dragon Quest fans are searching for evidence of his use of an emulator and criticizing him for his dishonesty.
He is also criticized for other reasons, but I do not provide a detailed explanation since it is not directly related to using an emulator. For more information, I recommend you to refer to the entry on Nicopedia (it is written in Japanese, though).