I originally wrote this in here to list some tips and tricks in some modes, but I ended up moving it here anyway since it becomes too long.

This is basically just a written tips for finishing the game in case anyone needs it. I also have a video for some achievements.

I'll list the section in the order of which mode I recommend you to play first. Note that most of these tips were written when I played in my potato laptop so some parts might look less difficult than how I wrote it.

That's a Good Start
Complete First Level


One Down
Destroy First Boss


FIN
Complete Horizon Shift



If it's your first time playing this game, you need to finish either Arcade or Arcade Arrange in order to unlock other modes. There are 34 waves (levels) in total.

Play Arcade Arrange instead of Arcade. You only have 1 life but there is a checkpoint in every level. Plus, if you experience the bug that sometimes make you fall of horizon in Wave 22+, it'll be almost impossible to finish the game in that state. I don't have detailed tips for each wave but here are some general tips:

• Kill all enemies if possible (especially in early levels)
  
• If you can't kill all enemies, prioritize the most annoying enemies first. Some levels have different enemies to prioritize, but you must always prioritize Swarms first.
  
• Try to figure out the killing order. If you die after killing the blue enemies before the red enemies, try to switch it around and see which one ensures your survival better.
  
• Use bomb whenever you can. You can save and use it when you're about to die, but make sure you really use it.
  
• Focus on survival if you think that you have been on the wave for quite a long time already. You only need to proceed to the next level and not racking up your score.
  
• Ignore the chain and score achievement for now.
  
• Jump. You can jump above the spikes, you can jump if you think it's save enough. Double jump if you're unsure. However, don't jump in boss fights except the last two bosses. Chances are that you'll die instead.
  
• Optional: read this guide. It's not much, but at least you know how the power up works by reading it.

There is a video for the Horizon Legend achievement in the "Other Achievements" section if you want to see the general gameplay, but don't follow it too much since the video focuses on racking up as much points as possible. Since I died in Wave 24-25 in the video, here's the replacement:
https://www.youtube.com/watch?v=uVj7h4aHOj8

I also died in Wave 31+, but I'm too lazy to record it since the game always run very slowly whenever I died and it somehow didn't save my progress in Arcade Arrange anymore. If you need tips on how to defeat the last boss, checkout the video in Boss Challenge section. Again, it won't be as accurate for Arcade / Arcade Arrange, but at least you have something.

Giant Killer
Complete Boss Challenge


Note that these tip might or might not work in Arcade because you get full weapon upgrade in this mode.

First boss: Just hit it until it dies. If you have any trouble, check my advice on the Tournament Mode section.

Second boss: Try to go a bit left or right from the center to dodge the ship's laser and stay on that area while dodging the yellow and red bullets. If you think that the laser is going to hit you in your spot, you can play it safe by going to the far left or right and hit the boss with 1/3 of your attack.

Third boss: The hardest boss IMO. Just attack it like usual on the first phase (those red beams). It'll shoot out yellow beams on second phase. Try to go to the opposite side of the area where the beam first shows up (if the beam spawns from the left, head a bit right to the center) while avoiding the white bullets. Move to the other position afterwards because it'll alternate the yellow beams until the third phase.

The third phase is the hardest. You basically have to dodge the boss' moving red beams. Try to practice moving a bit left and right to dodge the boss' attack (it took me hours just to get it right; you basically need to hold the left/right button not too fast, but not too long either) and hope that you're not lagging. After the red beam is done, the boss will shoot lasers. Again, you need to be lucky to not get hit since there are chances that you won't be able to dodge at all. You should know some of the safe spots if you played this level a lot. Sometimes you also need to double jump to the far left or right to dodge these.

Fourth boss: The first phase is simple. Just attack it and move to the left side while dodging the bullet whenever the boss is using the red beam attack.

On the second phase, start from the right side. Move to the left and back to the right since the boss will move that way. Make sure that you're on the top left of the boss when it spawns the red beam attack and dodge all of the white and yellow bullets coming your way. Just focus dodging afterward since you just need some hits before moving to the third phase.

Start on the top side on the third phase. Dodge the first wave of white bullet and stop shooting after it moves back to the right side (this is important). Hit the bottom side a bit afterward when it's about to shoot the red beam. If you did this right, the top boss should be moving slightly faster than the bottom one. Alternate attacking the top and bottom side from your leftmost side until the top boss is dead. If you did this right, the bottom boss should be moving slightly faster so that there are some spaces between the yellow bullets that you can pass through. Try to dodge the yellow bullets and kill the bottom boss afterward. Don't stay on the leftmost side; keep on moving while avoiding the bullets instead. You might even want to go to the top side a bit to dodge those red bullets.

Fifth boss: A bit of RNG here. The first phase might differ from time to time. If the boss' yellow bullets are passable, attack it from the middle while avoiding the bullets. If it's not, attack it from the sides (make sure you don't get hit by the laser and move to the opposite side when you think that you can't make it. Sometimes the yellow bullets will reach to the leftmost or rightmost corner and you won't be able to dodge because of that).

After this, the boss will keep on shifting between brick breaker (2, 4, 6) and yellow bullets phase (3, 5, 7).

The second phase should be easy. It's a brick breaker minigame. Make sure you don't hit the ball with the top right or top left corner of your ship or it'll bounce to the ground. Also, play it safe. if you think there's a chance you won't make it, just don't do it. Double jump instead to dodge the spikes. This phase should be over after 4-5 balls hit to the boss.

As for the third, fifth, and seventh phase, just keep on moving to the left and right from time to time (don't move too fast or it will be useless). Staying in one place will kill you. Also, even though there are a lot of bullets on the screen, it doesn't mean you can't pass it. Note that you won't die if your platform (that square thingy on top of your ship, idk what it's called) hits the yellow bullet.

For the other brick breaker phases (fouth and sixth), you just need to do the same as the second phase. The fourth phase will have a laser added (just double jump in the same place if you want to dodge a spike) while the sixth phase will have increased laser (3 instead of 2) and yellow bullets. You just need to make sure that your ship doesn't get hit and hit the ball to the boss. I don't think you need to alternate to the left and right in this phase since the bullets are randomized. If you're lucky, you'll survive.

https://www.youtube.com/watch?v=YDjNeNJpjgw

Wow!
Kill 2nd Boss in Tournament mode


I suggest to complete Boss Challenge first so you know how to deal with the first boss quickly. If you don't want to do that, here's my advice.

Wave 1-5: Easy, just make sure that nothing pass your horizons. If one of them passes, try to survive.

First boss: Start from the middle on each phase.

On the first phase, the boss will either fire the yellow bullets horizontally or diagonally. You're lucky if it goes horizontally. Just keep on firing until the bullet passes you and go to the boss' left side, dodging its red beam and yellow bullets until it moves on the next phase. If it goes diagonally, just try your best to hit it while dodging the yellow bullets.

On the second phase, the easiest is if the boss fires the bullet diagonally. Move to the boss' left side and hit it while dodging the yellow bullets. You might need to be more careful if it fires the bullet horizontally.

On the third phase, start from the top. Move to the boss' right side and keep on hitting it until it dies. Move to the bottom side afterward and hit the boss' right side a little bit and head all the way to the right when the boss moves to the right. It'll die before a bullet hits you.

Wave 7: Just let the ball drop to make it faster.

Wave 8-10: It'll be hard for you to kill everything in this wave so focus on survival if one of the enemy touches your horizon. You still can kill everything if you're lucky tho.

Wave 11: The laser is annoying. You need to choose a side (left/right). I usually choose the right side and if you choose the same side as me, make sure that the blue enemies in the beginning doesn't break your horizon on the right side and ignore the left side completely (do the other way around if you choose the right side). Try to hit any green enemies that is on the right side (be careful with the bullets) and stick to the rightmost side (leftmost side if you're on the left side) when things go rough. Hopefully the wave will be completed by then.

Wave 12: You need to pay an extra attention to the red monsters. They can die in a single hit so just sweep the screen whenever they come and focus on the green monsters afterward. Watch out for the bullets and make sure you destroy the Swarms that come right after. You can ignore everything afterward since the wave will be completed shortly after it (or just kill them, your call). FYI, I finished this wave after one red monster latched onto my horizon once so it's still doable if you screw up.

Wave 13: Last wave. You can die and get the achievement if you kill the boss on time. Try to follow my advice on the boss challenge above and pray that you're lucky enough to survive the RNG.

https://www.youtube.com/watch?v=71uIxaLTLGA

Flawless Victory
Perfect a Bonus Stage


Finish the first level of Shift-out mode.

Retro
Complete Shift-Out Mode


Note that you will lose a life if your extra ball that you get by breaking the Ball-Up block falls. If there are more than 1 ball that is about to touch the ground, prioritize saving the one that is moving slower.

Wave 1: Try to aim the 1000 blocks by bouncing the ball horizontally. Clear the rest of the blocks in the same way. Do not make the ball go diagonally since it'll make it harder to control. You should be able to finish the level by losing 1-2 lives (0 if you're very good, but I never did it personally).

Wave 2: Focus the ball on the blocks on each corner. Do your best to hit the blocks on the other corners if you finished it without dying. You should lose 3-4 lives at most.

Wave 3: Clear the 4 blocks below the 1000 blocks first. Bounce the ball diagonally near the leftmost or rightmost corner to aim for the Ball-Up and 1000 blocks. Focus on clearing the 1000 blocks. The rest of the blocks will be cleared that way. If you're struggled to move the ball to the 1000 block after you die, try moving a little bit to the left or right from 05:55. You should lose 2+ lives here.

Wave 4: Aim to break the middle and clear the blocks from there. I can't comment much about this since you just need to be careful.

Wave 5: Move the ball diagonally and avoid the yellow spinning block in the middle since it'll make your ball goes super fast for a while.

https://www.youtube.com/watch?v=MuHdyrlHpn8

Boom!
Bank a Chain Over 5,000


Big Boom!
Bank a Chain Over 10,000


1Up
Collect a 1Up


Horizon Hero
Score Over 100,000


Horizon Legend
Score Over 250,000



You should know what to expect after killing the second boss in Tournament Mode. Play Arcade from level 1 and let most of the blue and red enemies (especially on the first 7 levels) break or latch on the horizon. Use a bomb after your chain is 10k+ to get 2 achievements in one go. You'll get the other achievements after you reached a score of 250k.

You'll get your first 1-up after you reach 100k+ score. The hardest thing in these batch of achievements is reaching the 250k score, especially with the bug in Wave 22+. Try not to bank a chain unless you're about to reach the 250k score because the x2 powerup will multiply your chain score. You'll benefit from this greatly; imagine if you have 50k chain score and got this powerup - instant 100k score.

As for the x2 powerups, DON'T PICK THEM UP unless they're about to fall from your horizon. This is because you can maximize your score if you pick them later on. Don't worry, they will stuck on the floor and carry over to the next wave. The only time they might be unreachable is when the horizon moves around at Wave 22 or when you're on the third boss fight so make sure to pick it up before that.

Here's some pointers on what you should do. I just went along with the flow for the rest of the Waves (26+) and spammed bomb whenever it's available on Wave 28+

Wave 1: Wait until the chain goes to x5 before killing the others. If you do this right, you should have ~1k chain.
Wave 2: Let first 3-4 red enemies to latch on the horizon before killing the others.
Wave 3: Kill all enemies
Wave 4: Let first 3-4 red enemies to latch on the horizon before killing the others.
Wave 5: Kill everything.
Wave 6: Kill the boss normally. I usually got 10k score and 2.5k chain at this time.
Wave 7: Bonus round; try to get as many score as you can.

Wave 8: Let the first batch of blue enemies to break your horizon and kill the rest.
Wave 9: Let the first 3 red enemies to latch on the horizon and kill the rest.
Wave 10: Let one of the red enemies to latch and kill the rest. Don't go to the left side when it's almost close to the horizon.
Wave 11: Try to kill some of the blue enemies while letting some 1 or 2 of them breaks the horizon. The multiplier will increase over time since you won't be able to get them all. Make sure you protect one side so you can still go to the corner to hide though.
Wave 12: Let one of the enemies in the fourth batch to latch on the horizon and kill the rest. You might want to let some of the blue enemies to break the horizon while you destroy the swarm.
Wave 13: Kill the boss normally. I usually got 40k score and 10k chain at this time.
Wave 14: Bonus round; try to get as many score as you can.

Wave 15: Let one of the red enemies to latch after the second Swarms are about to come and kill the rest.
Wave 16: Let the first 3 red enemies to latch and kill the rest.
Wave 17: Kill everything.
Wave 18: Kill everything. You can try to let 1 enemy to latch but it'll be hard to dodge.
Wave 19: Kill everything. It might be tempting to let the red enemies to latch but I tend to die whenever I let them in.
Wave 20: Kill the boss normally. I usually got 90k score and 14k chain at this time. If you have trouble to kill the boss like me, use your bomb so that you won't lose your chain.
Wave 21: Bonus round; try to get as many score as you can.

Wave 22: Let one enemy to latch and kill the rest. Double jump or switch position whenever you want to dodge the enemy.
Wave 23+: Kill everything and use bombs if necessary.

From this statistic, you can get the 250k score if you get 4 2x powerups before the third boss on wave 20 (10k x2 = 20k x2 = 40k x2 = 80k x2 = 160k -> combine this with 90k score and you'll get 250k).

Anyway, here's the video if you fed up with my explanation:
https://www.youtube.com/watch?v=w19HJ7v8Axs

Well, I know that the guide is lacking but I hope it helped you somehow to finish this annoying game and its pesky achievements.