I have defeated Nightmare after running 793 meters. Not sure if all upgrades are necessary (as if, without them you won't get good ending, period.), but they are very, very, very useful.
Of course, combination of mushroom and "SURPRISE!" Fast Burning Skully is still irritating. :P
Also, apparently turning tutorial on helps with flawless 120 seconds. At least, it helped me. Flawless 199 seconds. Still not sure how.
5/5 - I hope you will enjoy this game. :)
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