Sekiro potential pre-Armored Warrior monkeyskip (not successful yet)

You can use the poison Mist Raven trick to reach over a deathplane in Senpou, right next to Kotaro. By dying from poison during the fall, you can land on the collision plane below the deathplane. You can then revive on it and run around a bit, but you'd still need a bit more reach on the final jump.