[Obsidian]

No Dream Avatar, unfortunately, however, there's an image-heavy list of items here.

As far as off-site trading, the only thing listed that is prohibited in Trisphee's Forum Rules is the trade of items and/or currency for items and/or currency on other sites, but I don't see anything about trading artwork on this site for items on another site or items on this site for artwork on another site. So best bet is probably to ask a Staff Member of that.