Some of the entrances throughout the map have an additional pixel you can stumble upon if you catch the timing right before you'll be sent to the next location (it doesn't change that much in confines of the gameplay, but it's a bit strange, that some of the entrances work this way, at a time others don't).

The next 2 screenshots are about the tiles, that at least by the way they look like, don't seem like collisions have been set right for them (1st screenshot has been taken at Snowdin - Town location, and I think most of people can agree, that this tile doesn't look like an obstacle; from the 2nd screenshot, like half of the alike-tiles don't have a collision at Hotland location, and it, on my mind, could fit in some of the cases, like if they're are located near vents or conveyor belts, but overall it doesn't make much of a sense to me, I'd say).

The next 4 screenshots are about vents and conveyor belts (1st screenshot has been taken at Hotland - Laboratory location, and it's a bit darker, as you can see : whenever you try to go up and change location using a conveyor belt there, you'll see your character at this spot for a moment, which is a bit weird, I'd say; and also, if you try to do an action like pressing Dance button or typing /afk in global chat while standing on that exact conveyor belt, you will be sent back to this exact position, as it is on the screenshot, and will remain in the exact same room. 2nd screenshot is about pressing C while standing on any conveyor belt - it will just freeze you at the spot you've pressed it till the moment, when you decide to close that menu. 3rd screenshot has been taken at the next location - upwards, and it's about, that if you decide to press the Dance button while trying to make your way back on a conveyor belt, you'll just be stuck there with the animation being displayed, until you decide to press the Dance button again (I believe it's also this way with the /afk command, but I couldn't type it on that conveyor belt, despite of many tries). 4th screenshot has been taken at Hotland - Leap Frog location (works with every vent in Hotland/Core), it's about, that if you press the Dance button while running into a vent with the right timing, you'll be launched into the air, having only one frame of your character's animation displayed (it'll end once you fall)).

The next 4 screenshots are about weird thing I've noticed about the Harlow character, and they're (screenshots) mostly about, that if you're standing at different positions around the room, the Harlow's face will change drastically sometimes.

And once again, that's all for now. I'm sorry for being not very professional while reporting these issues, I should've recorded how they occur, but I'm unable to do this at the moment, so I tried my best to explain what are they using text, and hopefully it was understandable. Once again, these aren't really the game-breaking bugs, but still, I think I should report them for, once again, the sake of better game experience.