Bloodborne has an interesting bug that allows you to defeat bosses fairly easily if you keep your PlayStation 4 on for 12 hours.
A reddit user named Meatballz discovered that if you leave the game running for 12 hours or more, the bosses' movesets are reduced a great deal, making most of the fights incredibly trivial. Due to what is presumed to be a memory leak, they no longer use their more complicated attack moves.
Meatballz discovered the bug during a marathon playthrough of Bloodborne. The player also discovered that restarting the console will restore the boss fights to their original state.
“I just tested this yesterday by turning off the PS4 power saving options and leaving Bloodborne running all night. Sure enough, when I played in the morning Logarius had transformed from an intense spell casting maniac into a senile old man who did nothing but attack with his scythe over and over,” he said.
Other users suggested that the bug can be replicated if you put the game in suspend mode.
There are two videos below that showcase one of the game's boss fights in regular mode, and one with the game having run for over 12 hours.
Regular mode
Easy mode