Here's my pointer for Monster X: Git gud.
Cave Story Tribute Site Forums
ColdCallerLoopy
Serri
Level 2 Sword is your best friend. Also, as soon as the battle begins, kill some Gaudis that would be in your way (mainly the shooting Gaudis)
mckgamer
Monster X was never too hard. It was just that when I DID die I had to go all the way back to the nurse. But I recommend using the knife. A lot.
ColdCallerLoopy
Also if you have the machine gun (Assuming you don't care about the spur), use that for extra propulsion when Monster X is moving back and forth.
And if you get low on hp in the first phase (like say 10 to 3 hp), make him go to the far left or right (assuming you killed all enemies in the current area), and pound some shots into the 4 ball-things, then after 2-3 shots, immediately run backwards and shoot at the remaining bullets, if you have the machine gun it makes quick work of those things. And on the second phase of the fight, use the blade at level 2 or 3 (varying on your style) and wail at the middle with everything you got and shot the greenfish-missiles, it's not too hard once you get used it, you just have to find a strategy that suits you, I hope mine helped.
And if you get low on hp in the first phase (like say 10 to 3 hp), make him go to the far left or right (assuming you killed all enemies in the current area), and pound some shots into the 4 ball-things, then after 2-3 shots, immediately run backwards and shoot at the remaining bullets, if you have the machine gun it makes quick work of those things. And on the second phase of the fight, use the blade at level 2 or 3 (varying on your style) and wail at the middle with everything you got and shot the greenfish-missiles, it's not too hard once you get used it, you just have to find a strategy that suits you, I hope mine helped.