I've been stuck for quite a while in Cave Story+, fighting the following boss (Monster X):

Boss: Monster X

Since I'm playing on hard I don't really get the chance to 'explore' what I'm supposed to do, as every hit is an instant death. When he starts shooting at me I can't seem to fend off all his projectiles, there are always some that come through.

Any pointers on how to hit/where to hit this boss?

  • I made the question more explicit, asking how to defeat the boss on hard. The tactic mentioned in the current answer does not work on hard. Commented Feb 18, 2012 at 15:33

3 Answers 3


Monster X actually consists of two phases, and you can only deal damage to his health during the second phase. In either phase though, you can only deal damage to Monster X when he moves away the armour concealing his weak point (pictured below).

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When his weak point is exposed, you need to destroy the 4-yellow orbs at each corner of the weak point. Once you destroy those, you'll enter the second phase of the fight. You'll finally be able to damage Monster X by hitting him in his weak point when it's exposed, similar to the first phase. Only this time you'll actually damage his health too.

He's a very tough boss, so don't be surprised if it takes you awhile to beat him. I'd highly suggest using the level 3 blade since it makes quick work of the missiles he fires at you. The level 3 bubbler also works well.

Here's a video of someone beating the boss, which may prove helpful:

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    Even spamming with the level 3 blade I die instantly. It can't seem to keep up with all the purple stuff flying at me. :-( Commented Feb 16, 2012 at 20:12
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    Finally I was able to make it through phase one! Using the maxed out machine gun shooting up (as in my answer) is a lot easier than using the blade. Furthermore, I don't have the bubbler yet, I only have polar star, machine gun, snake and the blade. Commented Feb 18, 2012 at 15:27
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    The video isn't helpful either, it's obvious it isn't recorded on hard, and he gets hit several times while shooting at the boss. Commented Feb 18, 2012 at 15:35
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    @StevenJeuris The new video is for a 3HP challenge, so that should prove more useful for future visitors.
    – Wipqozn
    Commented Feb 18, 2012 at 15:38
  • You are not alone. I was also working on the 3HP challenge: was relatively straightforward until it got really difficult fast, right at this point. Commented Nov 24, 2022 at 1:25

It took me ages to finally pass this boss ... but for those of you also stuck, here are a few tips I found out which allow you to save some time/prevent you from dying as quickly.

Getting to the boss

  1. Use the blade to quickly clean out the first few enemies in the first room from the savepoint.
  2. If you have a machine gun there is no need to clean out the entire room, you can jump and shoot down, giving you air and allowing you to go to the right immediately. This saves you plenty of time.
  3. Similarly you can avoid having to wait for the elevator to come down and up again.
  4. Be sure to clean out all the roaches and leave none behind, you'll have enough worries later on.
  5. The last few roaches you have to kill while the boss comes rolling in are best handled using the machine gun, while continuing running right to avoid being hit.

Boss phase 1

  1. For the first phase of the boss, just ride along while it's driving, and jump of right before it passes the fence. This gives you more space to run back while it's shooting at you.
  2. Use the blade to shoot at the center of the boss, and immediately run away. Stand still after a while, fend of bullets, and only after a while, start running again. This is essential in not getting hit.

Boss phase 2

For phase two it's best to fire while standing in between the tracks of the boss. It takes quite a while before the homing missiles reach you. Only worry about those once the boss starts moving again.

The following video shows what you're supposed to do, but hopefully the added tips here can help.



The best method I've found is to spam the blade 3 at him directly twice then run while spamming blade 3 even more to destroy the purple attacks. Repeat the process, try and get as far away as possible when avoiding the purple things. In phase 2 get under him and shoot blade 3 up until he close up, do as much damage as possible, get on one side and ride him and destroy the missiles at the same time, then repeat the process 2 more times, maybe 3 and he should die like that. Just keep trying, I know what a pain this fight is.

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