Shriek is the last boss of the game and on top of being RNG, her fight is also pretty long. Fortunately, there is a few ways to speed up the fight
Optimising damages
Once you finished the first phase, the game tricks you into thinking you can't damage Shriek anymore until you finish the escape but it's not actually the case. Even if you can't see her health bar anymore, it's still possible to to damage her and even kill her before you reach the end of the escape if you are dealing enough damages.
The first spot is right after the first phase. Shriek will become invincible for a short amount of time right when you finish the first phase but when she flies off you can hit her for a bit beofre the escape starts.
Once in the escape, there is a couple spots where you can hit her (you can open the image in a new tab if you need to zoom).
- Just as the end of the first platform, Shriek will fly above you for a short amount of time. You can either throw a projectile at her or using some verticality options in order to damage her with a melee weapon.
- Shriek will fly at the top of that branch and break it. You can climb that branch before she arrives and start damaging her
- Shriek will stomp on the floor. You can damage her for a short period of time here.
- When you almost reach the next platform, Shriek will dive into you. You can throw a projectile bellow you in order to damage her.
- While Shriek is coming from background, you can stand on the left of the bump and damage her from here
- This is where you will be able to deal the most damage to her. She will fly a bit before the platform and fire a laser. You can position yourself above that laser and hit her head.
- Once you enter the sand with Burrow, Shriek will stomp the wall, making it fall. If you quickly exit the sand after entering it, you can get a couple more hits.
It's pretty difficult to kill her during the escape in the normal and hard difficulties but Shriek doesn't regenerate her health at the start of the second combat phase so every damage you deal to her will speed up the next phase. It's also possible to skip the 2nd combat phase (which is the RNG one) by dealing enough damage to her but not quite enough to kill her during the escape.
Keep in mind that if you die during the 2nd phase, Shriek will have the same amount of health as if you didn't dealt any damage to her during the escape. If you managed to skip the 2nd combat phase, dying will respawn you at the start of the last phase.
Deflector
With Deflector, you can redirect the feathers Shriek throw at you by hitting them with Sword or Hammer. Redirecting those to Shriek deals insane amount of damages and, if you are lucky enough to get that pattern when the 2nd phase is almost done, you can even kill her during the 2nd phase by redirecting all her projectiles to her.
To redirect the most projectile, you want to be just in front of her head and swing when she's about to throw her feathers.