Hiding in a closet or cabinet can help shake the monster off your trail... but also forces you to sit in complete darkness, listening to its heavy breathing as it stands right outside. If you're lucky, you'll eventually hear it open the door and leave... Sometimes, though, in Version 5, it likes to wait, just to see if it can't fake you out. Getting into a wardrobe while it's in the room? Bad idea.
The jail cutscenes. Sure, the oni can't get through a locked door... but it can stare you down while shaking the bars. Oh, by the way? Not all jail cells lock. So you might close a barred door and think you're safe, only to have the monster push on through...
The final cutscene of the first version. Hiroshi, Kazuya and Megumi escape up the well, then go to untie the rope so that the oni can't follow. The oni tries to follow by clawing its way up barehanded.
The Oni's special ways of Leaning on the Fourth Wall. Mainly, its tendency to hide behind text boxes. In version 6, it manages to invade the inventory screen, too.
Version 5 includes what appears at first to be a Flashback explaining how Takeshi ended up hiding in the wardrobe at the start. It's not. And the oni's grinning when it busts the door open, exposing a mouth full of jagged teeth...
Ao Oni is, like Yume Nikki, a Japanese RPG made by a non-professional. It's a horror game where the hero, Hiroshi and three of his friends gets into an abandoned manor, only to be hunted down by the monster who lives here. With the classical horror-game scenario and the amateurish look of the game, it may not sound and look so creepy. Then you start playing the game... and quickly learn to lock the door every time you enter in a room because the monster (or "Blue Giant" as the title says) can enter in and well... Game Over screen. At the end, Hiroshi runs successfully out of the house... AND IT STILL FOLLOWS YOU OUTSIDE TO GET YOU.
In version 6 getting killed by the Oni turns you into an Oni as well. This results in some horrifying jumpscares as your friends turn out to be monstrosities in disguise.
The Blockman Oni that appears late in the game. Not only does it come completely out of nowhere, but it also likes to charge forward, forcing you to move to the side of it to avoid it. And if you think that you can just go back into the house to avoid it, one of the other Onis appears from the house, cutting you off.
The oni's design in the movie. It looks seriously scarred and deformed.
Very late in Version 6, you will enter a large room, only to be greeted by a very large group of very deformed Onis, all horrifying in their own way (ranging from a blue mass covered in eyes, to the aforementioned blockman). Oh, and they leave the jail cell they're in and come after you. And the door has locked itself behind you. When you do eventually leave, re-entering will reveal that they've all gone.