One of the best fights in "Prince of Persia" was born out of a constraint.
In 1989, Jordan Mechner was building "Prince of Persia" on the Apple II. Because the memory ran out with the Prince's animations and the levels, he had nothing left for another boss character.
Instead of trying to fit a new character into the game's memory, Mechner took the existing code for the Prince and flipped the image of the character. This created a shadow version that required no extra memory space.
The fight became one of the best in the game. The Prince against his own reflection. Even after the game was ported to other platforms with much bigger memory, Shadow Man remained.
"If memory had not been a constraint, I probably would have created all kinds of monsters and enemies in "Prince of Persia" to add a lot of variety, but because there was no room for any of that, I was forced to dig deeper and came up with Shadow Man, which ended up actually being kind of deeper and more satisfying."