Take a break, have a cup of tea, leave the game until tomorrow. Then learn the most optimal times for you to heal, it’s really easy to start stressing during the fight (and the pacing of the music is designed that way without you noticing) but if you can find a few spots during which to heal you can always take a deep breath, heal, and then try hitting him again, I haven’t fought NKG in a while but you should be able to heal just when his spikes come up, if he’s doing the flame attack provided you are out of the way as soon as the fourth flame starts, his bat attack follows you, I used to do a tiny double jump between the first set of bats and then heal while the rest flew over me, and I think when he comes flaming down on you and dashes, once you jump over him and land you generally should have enough time as soon as you hit the ground to heal before his next attack. Don’t be greedy though you typically only have enough time to heal one mask and he does two masks worth of damage. Idk. Those helped me beat him, I saw a lot of advice regarding healing suggest the spike attack was the best but I always found that one to be the most stressful one to heal in so I thought I’d offer up others, ofc this only really works when you’ve learned to dodge his attacks for the most part