I don't have a screenshot or video of this (and it's been fixed now), but I was working on a physics-based walk cycle for a 2D character a little while ago. Spamming the left and right buttons would cause you to lift off the ground and fly away...

In a previous GameDev community contest - a 72 hour one - I was rapidly trying to add enemies to the game about halfway through the contest, just wanting to have spiky enemies slide back and force horizontally across the screen that you have to dodge.

To my delight, they started moving around in smooth but erratically swirling patterns making for a much more interesting game. I left the bug in there.

The bug was caused by me calling Rotate() on the enemies, constantly spinning them around (so they look like spinning blades), and me also calling Move(x, y) on them. I didn't realize that the API's Move() function was relative to the orientation of the enemies, and so was moving them "forward" and "sideways" of the direction they were currently oriented in. For awhile it even looked like they somehow gained collision detection (they were bouncing off walls) - though I knew that wasn't possible, because they had zero collision code! The bouncing off walls was just coincidently the time their continual rotation made them turn around, and other enemies I saw later were going through the walls.

One graphical glitch I had in a space TBS game I made was an invalid pointer accidentally replacing a planet with my game's logo - which was about three times the size of what the planet was supposed to be. The logo was already unloaded from memory too, so as a new programmer, I was really surprised. That was the first real invalid pointer error I encountered - and since it wasn't crashing the game, it was very hard for me to pinpoint what had occurred.

The greatest bug I've ever witnessed was when I was working on Sims 2 DS. We had this thief character whose getaway vehicle is a shopping cart, which is spawned some distance away from him and races toward him, he jumps in, and rides off. But due to a combination of steering code, obstacle avoidance, and high speed, the cart ended up orbiting him at a long distance, trying to turn toward him but then moving forward so it needed to turn more. Every few seconds, you'd see the cart zip past on the horizon.

Kind of funny, but what amped it up to hilarious is that it turned out it was actually getting a tiny bit closer on each lap, and about 20 minutes later it was finally making small circles around him. We all watched as it spiraled in, and he finally hopped in and rode off into the sunset.

To my delight, they started moving around in smooth but erratically swirling patterns making for a much more interesting game. I left the bug in there.

The bug was caused by me calling Rotate() on the enemies, constantly spinning them around (so they look like spinning blades), and me also calling Move(x, y) on them. I didn't realize that the API's Move() function was relative to the orientation of the enemies, and so was moving them "forward" and "sideways" of the direction they were currently oriented in. For awhile it even looked like they somehow gained collision detection (they were bouncing off walls) - though I knew that wasn't possible, because they had zero collision code! The bouncing off walls was just coincidently the time their continual rotation made them turn around, and other enemies I saw later were going through the walls.

That's awesome! It's always hard to purposely design enemy behaviors that use cumulative effects like that, but it makes surprisingly fun gameplay. Predictable enough that you can accept it was your own fault if you get hit, but not predictable enough that it's easy to dodge.

Something that so happend to me today, playing around with some alpha blending settings:

Not, I did not feed my PC acid, though it looks like it ;) This is the effect of a certain alpha blending setting, which should result in subtractive blending. Well, almost.