"Tail plastic weird"
The tail on this figure is a rubber tail, with hard plastic plates on it. I'm not sure if it was just mine, but the tail pulled out of the one I have, due to the fairly-thin rubber (that anchors to a metal peg) tore.
A mint box generally has no noticeable flaws. This doesn't mean it is a C10 box, but that it doesn't have any significant damage to the box. It still may have wear to the window, and a small amount of wear to the box that is noticeable upon close inspection.
A C9 box is still considered very displayable and may have a kink, ding, minor fray to an edge, etc. The box is still case fresh and unopened with factory sealed tape on both sides.
By selecting this option, TFsource allows you to continue to add either instock or preorder items to your stack, as well as change how your orders ship out, which can save you on shipping!