Up until recently, it was impossible to unlock Vampire Survivors MissingNo secret playable character in-game. Instead you had to edit the game's code directly. Of course, this wasn't intended by the developers, who had removed the character in one of the early updates, but now you can unlock MissingNo by playing.
MissingNo is very similar to the Red Death character that replaced them, except that they start every level with random stats. So if you're ready to jump in and cause chaos—whether that's for the first time, or just the legitimate way—here's how to unlock MissingNo in Vampire Survivors.
Vampire Survivors MissingNo: How to unlock this playable character
To access MissingNo as a playable character, you'll first need to unlock the Yellow Sign. This is a hidden relic that you can get from the secret stage, Holy Forbidden. To access this stage, you need to survive for 14 minutes in Moongolow with a standard character and defeat the boss there.
Just be aware that when you enter Holy Forbidden, you'll lose all your armor and power-ups and will only be left with your starting weapon. It's useful to have a fast character here so you can get through the stage quickly and pick up the secret relic.
Once you've unlocked the Yellow Sign, you should make sure you have access to the Green Acres challenge stage. This is done by unlocking Hyper Mode for two stages. Once you have access to this, enter Green Acres with both Hurry Mode and Hyper Mode enabled.
Now you need to head southwest and you should soon see things start to change around you, like the game is glitching out. Large winged enemies will begin to appear and you need to kill at least 128 of them. Once you've made short work of them, head to the character selection screen and you should be able to buy MissingNo from there. Good job!
Interestingly, MissingNo seems to be a reference to a famous old glitch found in Pokemon Red and Blue, where the player could battle and catch a mysterious, deleted Pokemon by the same name. It would also cause weird abnormalities like increasing the number of items in a player's inventory by 128. The prerequisites for unlocking MissingNo suddenly seem far less random, huh?