Imrix
Periodically Malevolent QM
It looks like laughter. It smells like hunger. It sounds like indigo.
More seriously, it depends on the observer. For most people, it's a riot of conflicting sensations as their mind rebels at a world they were never meant to understand, but for a mercy it lasts only a few moments before they discorporate. Pure Chaos is fundamentally inimical to most forms of life.
On the other hand, for the Exalted and certain other powerful entities with the appropriate magical reinforcements to their sense of self, the Wyld is... Reactive. It looks like the observer believes it should look like, their subconscious mind imposing an idea of Shape and substance in order to navigate a Shapeless world.