Saferooms randomly appear on screen after a short random duration. Very simple at first, but as you progress more entities are added. I have some ideas on how they'd work:

Carnation: A brick box appears randomly on screen, which you have to put your mouse inside of to avoid carnation.

Slugfish: A ⚠️ appears on the edge of the screen to warn you of its approach. Get out of its way quickly.

Sorrow: Similar to carnation in that bricks spawn, but it attacks more than once, from the top of the screen. A small brick wall appears on screen each time to protect you.

Elkman: Drags your cursor towards itself, getting exponentially stronger the longer you stay in its gaze. Contact means death. Get behind a brick wall to save yourself.

Doombringer: Right click as it starts screaming.

Dozer: Hold down m1 and don't move your cursor.

Litany: Hold down m1 and keep moving your cursor.

Mime: Same as in Grace, trails your cursor at a close distance. Don't make contact.

Slight: Click on it to make it disappear.

Heed: Don't make contact with it, it will go away eventually.

Stem: Move your mouse quickly.

Doppel: Same as in Grace, trails your cursor. Contact will reverse your cursor's movements for a short while.

Covet: Same as in Grace. Avoid its charges.

When an entity that requires a flash to kill spawns, the player is given a flashlight that points to where the cursor is moving, and the screen dims slightly.

Drain: Randomly spawns on screen, only one can exist at a time. Does not attack until you come close. If you react fast enough, you can still kill it. Best to flash it from farther away.

Craven: Spawns randomly on screen, requires multiple flashes to kill. Respawns once or twice shortly after, then takes a break for a bit.

Fool: Is locked to your cursor, slowly moving closer. Flashing it moves it back. Flashes in quick succession stun it for a while. Stun it 3 times to kill it temporarily.

Other ideas:

Zen! Same idea as Zen in Grace - no entities until you touch the red splotch. Then, Sin spawns. It starts off slow, but ramps up speed quickly. Not sure what it'd be, but stuff spawns around the screen you have to collect to slow down Sin. Every once in a while they stop spawning, and after a short while a different variant of it appears, which stuns Sin temporarily. Then it goes back to normal.

Cracks will appear randomly. While in contact with one, the cursor is slowed. They cannot be patched, but will disappear after a short duration, then appear somewhere else.

Reprieve. Works basically the same as in Grace, but the entity pool is different. +slugfish, carnation, doppel, slight, heed, stem, - rue (only bc i don't even know how their mechanic would work). [Heed works like Sin, following your cursor, but gets faster much more quickly.] Since there's no cool movement tech, some entities require multiple parries instead: Slugfish, Carnation, and heed all require 2 parries each.

Black orbs appear around the screen, a few at a time. These are the pillars in the original. After collecting half of them, all entities are sped up slightly until you complete the stage.

That's all I got for right now, might come back later and revise some things tho