Two special ranks can only be won from crates, not bought.

Butterfly

The top rank on the server, won from the Butterfly Crate. It lasts 90 days, and using another Butterfly Rank voucher adds more time.

Ghost

A very rare prize from the Tricks & Treats crate. You get Serene perks plus a GHOST tag for 90 days. Using another one restarts the 90 days instead of adding to them.