The Entity has no particular appearance, but most players identify it as a black being with red eyes and a white cloak with a hood. The Entity can look like anything it wants to, be it person, animal, or object.
The only thing known about Entity 303's personality is that it is a form of pure evil. Its one desire is to send the world of Minecraft into one big glitch of chaos and destruction. However, it seems to take interest in appearing before players and scaring them, similar to Herobrine.
In "Minecraft Story Mode: Friendships Across Worlds," the Entity teams up with Herobrine to defeat the team who confront them, and they appear to be good allies.
These are the people the Entity is known to hate the most, as all they do is create, while it wants to destroy.
Entity 303 can shapeshift and turn into other forms. This is not limited to other players; the Entity can be an animal, an NPC, an object, or even a full-blown structure. It can also turn into black smoke, making it easier to sneak around.
Upon being an all-powerful glitch, the Entity always knows what's going on, and is quite knowledgeable for a monster of its stature.
When you don't care who you scare, kill, or mess around with, you make a lot of enemies. The Entity is a much-feared monster all around Minecraft, and a hated one at that.