Quetz'lun Is a spot in Zul'Drak with Scion of Quetz'lun - NPC - World of Warcraft and Altar Warden - NPC - World of Warcraft. Snakes drop trash and frostweave cloth and u can also skin them. The air elementals Drop Crystallized Air and Frostweave cloth. And they can both Drop Various Northrend Greens and Blues.
Best Way to do this is by mob tagging,Have a friend with you and pull multiple of those and then let him take them off you and kill them.Both the Snakes and the Air elementals Give around 5k XP(rested) wich is more then what a normal elite mob in a instance give.
Also If u have done the Quests in That zone you wont be able to kill them. The first quest is Seek the Wind Serpent Goddess - Quest - World of Warcraft so
Good luck.