An untimely glitch can ruin the cinematic immersion that videogame producers and developers have dedicated hefty budgets and thousands of hours to developing. Sure, gamers will forgive the occasional NPC walking into a tree, but even this minor offense derails the experience and reminds players that they are, in fact, playing a game. Most bugs rightly earn the ire of developers, producers, and gamers alike, but once in a while, something different happens. Some bugs find a niche and take on a life of their own.

The Team Fortress series began with a Quake mod. Players had to take advantage of the specialties and strengths of their teammates if they wanted to defeat the enemy team, so a degree of trust and familiarity between teammates was an absolute must. Unfortunately, the game engine occasionally rendered enemy players as allies due to a graphical glitch. As a result, players often turned a blind eye to an incoming ally, only to fall victim to unexpected friendly fire. The graphics error directly disrupted the team dynamic and led to otherwise impossible comebacks.

The Team Fortress bug gave its developers an idea: Create a new class with the express purpose of disrupting the enemy team's strategies. Using the display error as a basis, the Spy has the ability to disguise himself as a member of any class from any team.

The Spy added a new level of depth to Team Fortress. His Team Fortress II incarnation plays an important role in ending stalemates and eliminating key targets, acting as the wild card that reinforces the need for constant team communication.

The Spy wasn't the first glitch to be adopted as a genuine feature. Prior to the internet, many gamers gathered in local arcades to show off their skills. In 1992, Mortal Kombat was on the rise and young gamers across America were chomping at the bit to discover its many secrets. With no access to strategy guides or online FAQs, players had to discern special moves and fatalities through trial and error or word of mouth.

In most other fighting games of the era, the single player objective was to defeat computer-controlled opponents through a tournament ladder and ultimately defeat the boss. While this was certainly also Mortal Kombat's main single player objective, the game added a new element to keep players coming back. From time to time, a green ninja appeared before a round began, taunting players to find him. In rare instances, he would actually challenge the player to a fight and award a massive point bonus when defeated.