Pokemon R/B/Y - Stat down modifier overflow glitch (and a look at the quirks of stat modifiers)

At 2:08, there is an error in the blue arrow from +3 to +4. Since Pinsir doesn't yet have 999 attack before using Swords Dance, it will go straight to +5. This also means that the blue arrow from +4 to +5 doesn't need to be there.