After 2 hours of camping to get 3 trinkets for twinks, my conclusion is:
(1) Trinket of the scale always drops.
(2) PH of Dranadune can be any of mist drakes and itself.
(3) No interval time between respawn, it can pop soon after just been killed.
So, for this camp what you should do after arriving is to check if Dranadune is up already.
If not, start killing all mist drakes, then kill steam drakes since they may repop as mist drakes next round.
I know it will pop soon after I killed 7-8 mist drakes in a round.
Edited, Sep 7th 2011 4:49am by zight

Amber
Black Sapphire
Bloodstone
Blue Diamond
Dirty Vellum
Drake Blood
Drake Egg
Drake Meat
Drake Wing Bones
Drake Wing Webbing
Emerald
Grimy Fine Runic Parchment
Jade
Malachite
Pearlescent Drake Claw
Peridot
Serpent Spine Geode
Trinket of the Scale