Illusion

Illusion is an element that has appeared in various Sonic the Hedgehog games. They serve as power-up items and attacks for the player which serve to deceive an opponent(s)'s vision in gameplay.

Sonic Rivals series
In Sonic Rivals and Sonic Rivals 2, Illusion is one of the elemental Power-Ups that is useable to all playable characters. When affected, the player's screen turns grayscale and is heavily distorted, making it harder to see the level in gameplay. This effect only lasts temporarily. When used offensively, the user's Rival will be instantly affected by this and when used defensively, the user will drop a green spiralling orb of energy that will trigger the effect if their Rival runs into them.

Sonic Forces: Speed Battle
In Sonic Forces: Speed Battle, Illusion is one of the elemental effects which the Illusion Boost and Illusion Mine use to hinder their opponents. When hit, the player's screen flips horizontally temporarily, reversing the player's Quick Step controls when changing lanes. An icon will also appear near the top-center of the screen to indicate the reversed controls. These effects will only last temporarily. Illusion is notably one of the only effects that can affect players even if they are protected by the Shield or Invincibility.