Momodora: Reverie Under the Moonlight

To unlock the "Insane" difficulty you have to finish the game on hard. You don't need the true ending to unlock the mode and you don't need the true ending to unlock this achievement. All you have to do is to defeat the endboss.

In my opinion the achievement should have a higher ratio, but with all the checkpoints it's a matter of learning and patience... and skill, of course. In this difficulty you start with a very low amount of lifepoints and you can die with only a single hit. Your bow is your best friend and you should try to defeat enemys from the distance if you can.

You can obtain items from bosses if you defeat them without taking damage during the fight and with the lack of lifepoints you are more or less forced to defeat them in that way. Restart the fight if you take some damage and survive, especially if you have the chance to get some usefull stuff.

Some items can make your run a lot easier. I'll give a step by step list as a small roadmap for the most important items with a short description. I added my steps to map from the other guide here: https://1drv.ms/u/s!AnttpE0yt62MsRfQw8iW1SrI9P_f

Step 1 : Collect the Astral Charm to cut of some grinding time later. It's protected by a huge enemy. Use to pass him... afterwards he is easy to kill, but to pass him can be a bit risky.

Step 2 : Collect the Edea's Pearl after your first perfect boss fight. I love and hate this item. At this early stage is useful and beeing able to poison is sweet, but you can poison yourself which ends deadly and this happened to me many times. So use this item with caution. Use your bow for the boss fight and make sure to evade all his attacks.

Step 3: Buy the Crystal Seed for 80 munny star at shopkeeper A. This item can help you in the early boss fights and give you a 50% attack boost.

Step 4: Collect the Bakman Patch after the perfect boss fight. Before you drop down to the boss, make sure to open the shortcut and save your game. Poison the boss in phase 1 and just shoot arrows from a good distance. In phase 2 you should use your 50% attack boost and leaf to attack her boobs. You probably need a couple of attempts, until you figure how to evade all the attacks. The Bakman Patch can be really useful in some boss fights like the one with the bow guy and girl. With 2 full hits she lost around 75% of her energy. The only bad thing about the item is the summon time. You are unproteced for a couple of seconds and should try to use it at situations with a short waiting time or right at the start of the boss fight.

Step 5: Collect 700 munny stars. I killed the 2 enemys in the room right next to shop E room. You can use Bakman Patch to kill the enemys and refill this attack at the save point. It's probably not the best grinding spot, but i used this place because the shop with the item is nearby and my goal was to benefit as early as possible from the necklace to make this run easier.

Step 6: Buy the Neclace of Sacrifice. This item give you 100% attack power if you have low amount of health. You should have this bonus even fully healed and this makes this item so handy. If you collect too many hearts, you can lose this "always on" effect. That happened to me and i had to use the tissue item to damage myself to reactive the effect, because most other enemys killed me with a single hit.

Step 7: Collect the Sparse Thread after the perfect boss fight. Make sure to open the shortcut and save your game first. You probably saw the rockets blocking the door. If you stand above the door an enemy should bomb these rocks away and open the way to the shortcut. The boss fight should be not that hard. Sometimes i got killed by the big laser beam, but if you press down to duck, you can shoot from the distance and with the power of the necklace you should be able to defeat him in a short time. The Sparse Thread can be handy for some boss fights. I know the attack doesn't look impressive, but can deal a good amount of damage. You can kill the knight miniboss with these 2 hits and it also helped me to defeat the big breasted enemy in the battle before you enter the cat form for the first time.

Step 8: Collect the Bloodstained Tissues. You can have 4 total. You find a couple just on the floor at a deadend and you can get the other couple as a perfect boss fight reward. You can sacrifce lifepoints for a 100% damage boost. If you use the item 3 times, you have a 300% damage boost! If you use it 4 times without healing you will probably die. I'm not sure if you lose 25% or a specific amount of your lifepoints. You have to use the item BEFORE you trigger a boss fight. Otherwise the damage you take mess up your perfect win.

Step 9: Collect Pocket Incensory and equip it. This item let shoot you fire arrows and stagger your enemys. I replaced it with the poison effect and used in combination with the necklace.

Step 10: Collect all other fragments and defeat the final boss. Without Spring Leaf there are only 2 phases instead of 3. In Phase 1 it's not that hard to evade the attack and with a boosted attack power you can do a good amount of damage with your bow. For phase 2 i used the Bakman Patch, because the boss stayed at the center for a long time and lost more than 50% of his energy with 2 of these attacks.

If you need a visual solution, watch this youtube video here: It's not my video and this run ignore not all, but some of my steps listed above, but it can give you some boss fight tactics and shows you have to pass tricky passages.

That's all i have to add. If you have questions, feel free to leave a comment. Thx for reading and good luck!

Kugare's solution is great and cover all the topics needed to beat this. I'll just simply write some guidelines for the bosses and how to beat team without losing a life. So the first 2 bosses are actually the only ones were you either have only 50% bonus dmg or none.
Disclaimer: The bow was my weapon of choice in this game and is really good against some bosses, medíocre againt others and won't work againt 4(counting minibosses). So in this guide I'll focus on it: its safer, its reliable and most of the upgrades mid-game are for it rather than the Maple Leaf. I'll also suggest a boss order, but you can do them in any order (but some will be definitely more hard).

Edea: The first boss is quite easy ( I think the area imps are way more dangerous than it). Her tail attack is easy to escape if you're not right in front of her. I just stood a safe distance from her, but no too far, and jump and shot na arrow to its face, repeating until its dead. When it charges with the tail attack go back a bit press down and shot an arrow to its yellow core dealing some nice damage. Don't stick to either side of the map, as when it gets HP<50% she will release poison fumes that will kill you instantly. Her item drop is quite good against the normal enemies in the next areas but with the exception of some bosses (and I'll point them out) it’s risky, especially if you want to get the bosses drops (and you want, at least most of them). Drop: Edea's Pearl.

Moka + Lubella, the Witch of Decay: For this boss you'll have access to the Crystal Seed, save it for when you battle Lullabela. Moka is quite easy and it's one of the bosses where the Leaf is way better than the bow, at least at the start. Smack him with the leaf and when he charges his attack back off and deliver some arrows. By doing this, one of his attacks, the homing orbs that explodes, won't be cast and the battle is 100% safe. After chipping 50% of his life Lubella will appear. You can use the Crystal Seed now. She is also easy, especially since you beat her on Hard mode and knows her attacks. I'll list them here for you:
Orbs - She summons 4 orbs around her head and send them to the ground in their exact position. Just stand in the open spots betweeen them and you'll dodge it.
Homing Orbs - Lubella will move away from the battefield and 4 orbs will (slowly) enter the stage. After a blink they will all rush towards you. Do a dodge roll after the blink and you'll avoid them.
Explosion - If the ground beneath you shines move away from it as some Orbs will be summoned there and will float away, leaving the screen. Whenever you see the blink roll away.
Drop: Bakman's Patch. You have to beat them without taking damage as the item they drop will make one of the future battles (in my opinion, the hardest one) really easy.

Now the path splits up: there are 4 bosses and 1 miniboss that you can defeat in mostly any order you like. In this guide we'll head towards the monastery so we'll fight the miniboss first.

Knight: This "miniboss" is really easy. He is imune to arrows so you'll have to use the leaf to whack him. As soon as he appears on the left side of the screen slam him 3 times with the leaf. Roll back and wait for him to jump in front of you. Hit him again, roll back and wait for the jump. Repeat 4 or 5 times and its done. You don't need to be afraid of damage from him (tough you'll most probably die from a single touch) as he doesn't drop anything.

The reason I sent you to the monastery is because you want Tainted Missive. This item gives you 100% damage while consuming some life. You need the monastery key and then ride the elevator up and go left. In the room with the giant monster there's a shiny spot on the floor, that's 2 of these items. The tactics from now on, as Kugare suggested, is to use this item, then bellflowers, before entering any boss room. Despite being close to one of the bosses we'll skip her and go to the Cinder Chamber area, south of the monastery (you need to go down some really long stairs).

Heretical Arsonist: There are 2 entrances to this boss room. It doesn't really matter which way you go in, but dropping down the celling is faster (especially if you have the item that lets your arrows Pierce through the first enemy). As soon as you enter the room stand between the 2 sets of barrels that are there and shoot them both, this will make this battle a lot easier. Some people have some hard time against this boss and I believe it’s due to the Leaf. Forget about the Leaf for this fight the bow is all you need. As soon as the boss appears it will use a charge attack on the Knight that's fighting with you. If you used the Tainted Missives at the start you'll deal a lot of damage to the boss by just spamming the arrows at the start. This boss has a few attacks under her sleeve:
Homing Fireballs/Fire Columns - The most feared attack. The boss will send some fireballs to your current position and they will become fire columns with a boss teleportation with it. Don't go to the screen border as it can lock you up allowing the boss to hit you or to be killed by the attack itself. As soon as the balls are near you roll back as they will stop at your older position and explode.
Charge Attack - The boss will enter in a position of charging KI and will unleash one of 2 attacks: Various columns will appear at her position or she will summon some balls that will bounce of the floor. Both of these attacks are really safe if you keep your distance from the boss.
Whip attack - If you stay close to her she will use her whip sometimes. It has a somewhat area of effect so be sure to be far. The attack animation is really slow so it's easy to dodge this.
Flames - Wherever she uses a flame attack there is a chance of flames appearing. Just be aware of them.
She has one of the most important items: Pocket Incensory. This item should not leave your passive slot for now on against any boss. It adds Fire damage to your attacks, both the Leaf and the Bow. The arrow can now make most enemies flinch, and this includes our next boss: Fennel.

Fennel: she is located at the cathedral. Without the Pocket Incensory the battle is still doable, but may take a longer time. Plus, now that you killed Heretical Arsonist you have air dash, which is good against her. The strategy is to use the arrows for the whole battle: as soon as she approaches you jump+dash away. She will flinch for half the battle. When she changes to the second form use the Crystal Seed to finish her quickly. Her attacks are quite predictable:
Lightening – Some lightnings will appear on your position briefly and then will hit. As soon as you see the lightening roll away, preferably towards Fennel so she doesn’t corner you.
Curse jump – Fennel will jump forward and hit the floor with her sword, applying a curse if you`re inside the affected area. This is not so bad as very few items are usable here. If she miss you just spam arrows.
Dash attack 2/3 – She will dash forward and hit either twice (if HP > 50%) or thrice (if HP < 50%). The double attack can be dodged with a well-timed double jump, the triple attack has to be avoided with a roll or an air dash. She drops Tainted Missive, 2 more to a total of 4.

Derelict Frida: She is located at the Underground Grave (I think this is the area name). She is actually quite easy and I suggest using the poison arrow upgrade. The strategy is quite easy: enter the boss room, press down and spam arrows. You won`t be able to dodge one of her attacks this way but the buildup is so slow that it becomes easy to dodge. This attack occurs when she start attracting red squares in front of her. To avoid it you have to move to her other side. That’s it, her other 2 attacks will be avoided by staying low. She drops Sparse Thread which isn’t that much useful.

Lubella 2: Lubella is in the Whiteleaf Garden and the battle is pretty much equal to the first one, but now her attacks all have variatons:
The homing orbs now has 2 rows, meaning that you have to dodge roll at a more precise time, the explosion orbs from the ground come in 3 rounds and the orbs she summons have 3 variations. The battle is pretty much the same, she does reduce the map area when her HP<50%. It’s more of a memory battle: try to remember her attacks and you’ll beat her eventually. Try to enter the field with a lvl 3 charged arrows which, combined with the +100% x2, will deal a lot of damage to her, around 40% of her HP. Try to whack her with the leaf whenever you can. She drops Torn Branch which is quite useless in this mode.

Duquess Lupiar and Magnolia: This is a hard fight by all means. Lupiar attacks are not so predictable and if you don't exploit her weakness this can be a long grind. To kill her quickly: Bakman's Patch. It does a lot of damage on Lupiar if you get her right on the middle of it: I used the 2 charges and she lost more than 90% of her life. It's quite easy to use it well, just lure her to one side of the screen and start using the item (which has a slow using animation). Arrows do no damage to her so don’t bother using it. Wait for her to finish her attacks and, to be absolutely sure, just whack her once with the leaf rolling away as soon as possible.
Magnolia is easy: she'll teleport to you, try to stab you as quick as a tortoise and then teleport away leaving 2 damaging spheres. Just jump around the map and staying at a safe distance spam arrows. She drops Heavy Arrows which is a good item against the last boss remaining.

Sucubbus (?): She’ll appear along with some illusions and use a homing magic spell on you from all of her copies. Don’t let her do that. As soon as she appears hit her (she is usually the one flying closer to the ground). If she is too far away just hit an illusion and run away her attack area is high but it’s slow and you can evade it with the air dash. She is immune to arrows and doesn’t drop anything.

The Queen: she has 3 forms. The first 2 have similar moves and are quite easy to dispatch. The last form has a mix of Moka and Lubella spells. The first 2 forms spells are:
Homing Triangle - Sends a triangle to your current position that multiplies and deals heavy damage, possibly one-hit killing you. Just don’t stick to the end of the map when she uses it.
Bouncing Triangles – She becomes a traingles that bounces at the screen. Now you should stick to one side of the screen as it will not go through it. When it finishes bouncing it will slam the ground but staying on the screen edge is still good as she won't hit you there.
Teleport – Her basic attack. A circle will shine where you are before she appears there. It doesn’t do a lot of damage so it’s not a big deal. Try to make her teleport at the edges of the screen.
Tri-triangle – She will teleport mid-screen and summon triangles both at her sides and below her, moving to one of the triangles damaging anything in-between. Just don’t keep jumping and hitting her as she will most probably rush in your direction and will damage you.
Fast Moving – From time to time she will release a homing triangle and then rush to your direction on the screen. To avoid being hit I ducked after a few arrows and she missed all the time.
Triangle Spiral (Form 2) – In form 2 she will go to to the center of the screen and summon 2 triangles spirals at both her sides. Stay beneath her and whack her until the spirals are really close. When the jump is risky charge a lvl 3 arrow and go to the right side (the first to finish spiraling) to damage her. She finishes with a ground slam with some damaging orbs that are limited to that area.
The last form has these spells:
Exploding Triangles – She will summon 2 triangles at her sides and both will explode, killing you. Just stay with her and whack with the leaf.
Following Missile(s) – She charges a spell and when a circle shines dodge the incoming missile or missiles and keep whacking her.
Exploding Orbs – The ground beneath her will shine and 4 spheres will come out of it, just like Lubella. Just stay at her sides and send arrows her way. She usually uses this spells in this order so it's easier to know what to expect.
She drops an item Birthstone, that will only appear on New Game +, and doesn’t have any effect. It’s more like a trophy. So if you don’t plan to play this game anymore after this you can take a few hits.

That's it. I hope this guide makes some bosses easier (especially Lupiar). As for questions: I’m already forgetting about the bosses, 1 day after playing, so in 1 month I won't remember anything. There’s a nice guide in steam that has a different progression and all secrets location which can be useful if you get lost:

http://steamcommunity.com/sharedfiles/filedetails/?id=638712...

Welcome

In addition to the other great solution here is a video for beating bosses on Insane mode it has some good strategies.

Important: Make sure to get the item "Necklace of Sacrifice" it will increase your attack by 100% if your health is low which is always the case on insane mode, You can buy it from shop guy on "Subterranean Cave".

Remember to use some good spells during some boss fights they can speed things up.

Credits goes to ahmz1404 channel