There are 4 different prints in Sb, 3 character prints and one merc print. they are not interchangeable, you can not use a character print on a merc or a merc print on a character.

The way to tell the difference between the prints, is to go into your packpack and click on the print that you want to use and make sure it is the right print, you can tell what class print it is and why it may not be showing when you try to upgrade the character or mercs items.

Hunter Print
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Mage print
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Warrior Print
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Merc print
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The Wraithbone elite dungeon has more than one weapon boss, one drops merc prints, the other drops the character print, this is the BLUE prints that are dropped in the Dungeon, so you need to clear all the dungeons in Wraithbone to get all of the prints