Here is my 100% Achievement guide for Bullet Beat!
Beat level 4, put it casual, full walkthrough of the game.
There is one point in this ledvel where a big square of blocks are in your way.
What you need to do is, find the ONE block you can actually hit and keep hitting it.
The rest are invisible and you cannot shoot them.
You can tell which one your hitting as small bits of debris or something fall off it when you shoot it.
Hope This Helps!
Level Timestamps:-
Level 1 - 0:40
Level 2 - 3:50
Level 3 - 7:30
Level 4 - 10:25Level 5 - 14:55
Level 6 - 18:10
Combo 500 & 1000 Achievements - 20:05
Level 7 - 21:30
Level 8.1 - 24:20
Level 8.2 - 26:20
Level 8.3 - 30:00