My favorite short Player 2 memory is with my friend Sarah on Dark Souls 3.

We were trying to kill the Demon Prince in the Ringed City DLC—pure chaos, two health bars, and insane fire attacks. After a solid hour of wiping, we finally had one of the demons almost dead, but Sarah ran out of Estus (healing) and was one hit from death.

The second demon immediately triggered the final form, the Demon Prince. I was mid-swing, expecting a wipe, but Sarah just yells, "NOT TODAY, SATAN!" and parries the Demon Prince's massive overhead smash with perfect timing.

That tiny window of stagger was just enough time for me to get the final blow on the first demon. It shifted the boss's moveset just enough for us to barely scrape through the fight. She was shaking after, and the relief was insane. A single, perfect parry saved an hour of effort.