There’ll be some occasional consumable items you get from the battle pass that you can’t get anywhere else and won’t be able to get again (like, for example, a stack of 5 potions that let you use a single specific spell)
Soul Remnants are harvested from thralls you toss onto a sacrificial altar (new buildable with 3.0) and are consumed when corrupting your perks. They are always harvestable as they are a part of the core mechanics of the update. They have an icon similar to a potion you get from first couple pages of the battle pass, but are a brighter green and don’t have a skull in them.

Casting an illusion on an item to change its appearance is also a core mechanic of sorcery and may always be performed as long as you have the required crafting station built, as well as meet the requirements for the process (that is, the item you want the appearance of must be one you know how to craft, and must be of the same type as the weapon you want to apply the appearance to).
There will be special items that can, for example, be earned through the battle pass that can be consumed to grant an appearance without having to eat a weapon or know how to craft it. Those will not be required to access the base feature in any way.