They weren't actual demons, so he wouldn't be able to increase the spiritual quality of Thal'Korr and the incubus. But he could steal their spiritual power and gain a little extra strength during the battle.
He began the battle with the Power Amplification skill, while silver wings formed on his back. He flew around, dodging the attacks of the many Spirits that were focused on him while pirouetting in the air.
The Silver-Winged Leopard unleashed its anger at having fallen earlier on the surrounding enemies, destroying the first one in its path with a single blow.
Its great wings flapping, it flew off in much the same way as Liam, heading for the second of the enemies.