Vista-tan/Longhorn-tan

Ok, so, could someone say who is who? I noticed that some guy removed the vista tag and added longhorn, but checking the longhorn pics, she doesnt really look like the recent 'vista' pics, so, is that guy some troll, or was i totally wrong to tag the drill-haired, dark-skinned girl as 'vista'?

The guy who swapped vista to longhorn:
http://danbooru.donmai.us/post_tag_history?page=1&user_id=19932

Longhorn:
http://danbooru.donmai.us/post?page=4&tags=longhorn

Vista:
http://danbooru.donmai.us/post/index?tags=vista

Every artist on Pixiv I've seen with a picture of her, tags her as VISTA or ビスたけ. So I can't really see WHY WOULD YOU DO THIS, AYU

Yeah, troll or ignoramus. The grey-haired girl with the screw in her head is vista-tan (the screw is a pun based on her name if I remember correctly).

As far as I know, Longhorn doesn't really have a consistent design.