Hallucigenia (ハルキゲニア)

Overview
Hallucigenia (ハルキゲニア) is a fangame by Trendy-Sabamiso (トレンディ鯖味噌), a contributor to Yume 2kki (ゆめ2っき). It stars two young girls named Aya (あや) and Aine (あいね).

Gameplay
The game starts from Aya's perspective in an inescapable, mostly barren room. The dream world is accessed through a black book on her bed, her appearance changing outside of reality.

After completing certain tasks in Aya's dream world, Aine becomes a playable character. Aine's dream world is very similar to Aya's dream world, but is grayscale due to her colorblindness.

Unlike most fangames, Hallucigenia lacks background music, and has only a handful of sound effects.

In older versions of the game effects were referred to as Colors.

Plot
Aya enters her dream world from the black book on her bed. When in the dreamworld you are still Aya, but her appearance changes, some theorizing this has

Aine enters her dream world by sleeping on the bed. She lost her right arm, and she is also colorblind that she sees things in grayscale, either in reality or the dream world.

Effects
You can do actions with certain effects by long pressing Z.

Aya
Holding Z without an effect makes Aya's body distort.

Colors (Original Effects)
These were Aya's effects before version 0.006. In version 0.004, the effects lacked button actions and the Blue effect looked different. In version 0.005a, there was an effect action button in the Items menu. All of Aya's sprites were missing eyes in these versions, but there was a hidden patch in the GameOver folder giving her sprites eyes.

Aine
Holding Z without an effect makes Aine look at her lost right arm.