UnderCurve said:
I want to make a Tag for Venti's true form, im think of using Barbatos_(genshin_impact) as it would be similar to Rex_lapis_(genshin_impact)
Sounds good to me, otherwise it might need to be a spoiler like venti_(spirit)_(genshin_impact).
UnderCurve said:
Also I want to make a tag for his friend, an unnamed character that looks similar to Venti, unnamed_bard_(genshin_impact)?
The most common appellation for this character is probably "Nameless Bard." It's used on the fandom wiki, for example. However, nothing official exists (he's usually just referred to as 'boy' or 'lad' when he's mentioned,) so it's down to aesthetic preference.
There's another problem in that it's quite difficult to tell him apart from Venti, Judging from the story teaser he had completely black hair, unlike Venti's multicolored hair. That and artist commentary may be the only way to distinguish the two. I think some art on Danbooru currently tagged Venti like post #4411153 is actually of him.
However it's entirely possible that some artists have just drawn Venti without green-tinted hair, or have drawn him together with his wind spirit form (like how Zhongli is often drawn together with his dragon form.)
As an aside, I looked through Pixiv and couldn't find any tags in use for either of these. There's a #巴巴托斯 tag (Chinese for Barbatos) but it seems to just be used on random images of Venti.