Hollow Knight - Nightmare King Grimm

At the moment I am trying to defeat the Pantheon of Hallownest, a ridiculous boss rush challenge in which 40 bosses must be defeated consecutively. For a challenge like this, it's very important to practise the harder bosses until you can defeat them consistently, as losing to them in an actual attempt would mean starting the entire challenge again. In addition, several of the later bosses do double damage, giving you much less room for mistakes.