During the battle royale in Yu Gi Oh East Academy, Marcus screws up his entire strategy twice by misreading his own cards.
Destroy The Godmodder has many such events, the first notable one being the reapers. A massive army of them gets summoned, what happens? The godmodder mind controls them into changing sides. It isn't the worst offender either.
It turns into this for the godmodder later on, and everyone gets a slice of the action with the Glitch.
The Virus in game 2. Seems like a great idea, it gives the A Gs a fair boost... and then gains self awareness. And decides it wants to kill everything.