About when SpellVisual Applies to Object

[demonguy]

function at 0x4B6ED0(rebased in 16016) is a function which Wow calls when SpellVisual Applies to Object, it's a thiscall function and first argument is the Object address, the second is Spell_C object address... but what puzzled me is that , in 4.3.4 the first argument is truely a Player or NPC object...
but in 5.0.1, assuming unkObj is the first argument... *(__int64 *)(unkObj + 0x8) is the GUID of the object ... So isn't it a object address? should 0x8 be descriptor? why it's GUID