Yeah noticed that males doesn't have the same transformation :P Makes it even weirder. And yes, it's probably as simple as that, new voice actor.
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Yeah, and as ogren pointed out, only female Void Elves have this change. Maybe the Void do have some good reasons for this. Or not!
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Tyrande as well, she got like 4 different accent, depending on location/expansion etc. It can definitely be that it's because of what you say, that's how it is in real life too, though in some situations it's probably as simple as different voice actors. Nothing biggie though, but funny anyway.