Floating Chair

When an interaction with a chair gets cancelled during the sit down animation, usually by landing on the ground, Sybil stops being affected by gravity. The usual way to do this is to stand on an elevated ledge close to the chair. When then trying to sit, you may land on the ground during the animation and immediately start being able to move. You stay in the sitting animation until you attack.

To cancel out of a Floating Chair, you can either do a skid jump or use Sunsetter.

Standalone Randomizer

In the standalone randomizer by spuds you can find chairs floating in the air if they are randomized. You can start a Floating Chair from many of those by just sitting on them. It is unclear why these trigger it while on ground chairs need you to land.