Panther Thralls are essentially 'zombie' panthers. They have a tattered, dull grey/brown appearance. They have blue glowing eyes and when shot, they emit blue 'clouds'. They are similar to the Tiger Thrall.
Panther Thralls go for a kill first, think later approach. They will charge, scratch and bite Lara. The Shotgun is very effective against them being able to take one down in two-four shots. Adrenaline Headshots can kill a Panther Thrall in one shot as can sticky grenades. Once a Panther Thrall is down be sure to 'stomp' them to destroy their skeletons, killing them permanently. (If one of them is destroyed by the headshot or sticky grenade, it smashes the skeleton automatically, so no need to stomp.)