Infected shadow
After Quinn used the shadow infect skill, a creepy light purple shadow appeared out of Quinn's very body. It was a different colour from what it usually would have been when using his shadow skills, and at the same time, the way it came out of his body was also different.
When Quinn used shadow skills before, it would rise up from his own shadow at the bottom of his feet and engulf his back. He would keep a light, almost invisible shadow surrounding his body and grow and lessen it whenever he needed it.
This was what allowed Quinn to use his shadow powers the quickest and also helped him block attacks. Another thing to note was while using it this way, Quinn also felt that if he was in a fight and was to block an attack or such, he could use it this way as well.
It was easy to do because it was almost the same as when he used the second stage of Qi. Combining this with the shadow allowed him to use its solid form in the first place.