The Rimed Shell is an Exotic Ghost shell that can be acquired by preordering Beyond Light.

How do you get exotic ghost shells in Destiny 2?

Most Ghost Shells are acquired from Eververse either from her storefront or through Bright Engrams. However, there are a few Ghost Shells that are earned through events or pinnacle activities. Once you have obtained a certain type of Ghost Shell, you can reobtain it from your Collections menu under the Equipment tab.

What is the rarest Ghost Shell in Destiny 2?

The actual rarest ghost shell is a variant of the last city shell (damaged). For the new light players or the OG's that just forgot, when you started a new character in D2 you character started out with a basic white (common) last city shell.