These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Game Breaker: When DOUBLEBREAK was introduced to the 0.30 trial (the one released at Comiket 78 rather than the earlier 0.20 trial), the developer did not adjust the extend points, resulting in hilarious amounts of extra lives. The final version adjusts extends so that you no longer have as many as 10 lives by the end of stage 1.
Also, the Type-Z ship. This ship get the most powerful regular shot of all 3 ships, the widest attack range, and the Break bar fills ridiculously fast the moment you reach 50%. There are only two problems: first, you have to have reached the staff roll, and its price in the limitter shop is not very cheap.
To put that 3 million point price tag thing in perspective, Unlimited Mode is 300,000. If you were to finish the game 3 times (Beating Gorgoneion on your first credit), once on each difficulty, you'd still be short.
On a different note, it IS possible (though exceedingly unlikely) to end up in a death loop where you cannot escape. How is this possible when you're given Mercy Invincibility when you respawn? The invincibility doesn't kick in until one frame AFTER you respawn, and the game does a collision check on the frame you respawn. If there's a bullet right on your hitbox when you respawn...