The bug

Using a cauldron, layers can be removed from ominous banners.

Once two layers are removed, these banners can be copied, to create new banners with the name and color of an ominous banner.

A player can also add other dyes to an ominous banner with more than three layers removed, so that they can customize their own banners while keeping the name and color of an ominous banner.

Ominous banners taken from a raid can be customized while keeping their patterns hidden, as ominous banners from a raid do not show what patterns they are made up of.

How to reproduce

1. Obtain an ominous banner from a raid
2. Remove all layers from the banner using a water cauldron
3. Add other dyes and patterns to the banner
   The color and name of the banner are kept, and the custom patterns are hidden