"Checking is done both domestically and overseas, so for a game like Smash Bros., several hundred people are employed. So, debugging alone becomes a huge project. So much so that one of the biggest reasons for the separate release dates for the 3DS and Wii U versions was so that we could shift the debugging periods."
As gamers, we are able to laugh at funny glitches, and yell at developers over game-breaking bugs that are stumbled upon by accident, but very few of us are subjected to the process of actually finding them. With a game like Smash Bros., the varying combinations and complex coding involved is mind-blowing.
"In a previous Smash Bros., we found a bug during the debugging process where if fighter A hits item B and fighters C and D are simultaneously affected, the game would freeze. Considering not only the different fighters, but items, stages, color settings, play rules, and game modes, the number of varying combinations are astronomical. In order to properly debug, every pattern must be tried, but such a task would be impossible no matter how many decades or centuries you take.
There are many reasons why a game's release date will be delayed, but eight or nine times out of ten, it's usually because a bug couldn't be fixed in time. But it's better than releasing a product like that."
- Masahiro Sakurai