A Super Shue is the result of breeding 2 shues. The newly bred Super Shue will have both the parents' options and will have an additional option for "Critical attack". It is possible to breed 2 shues of different classes into a super shue of either of the parents' class.
To breed a Super Shue, the 2 parent shues have to be of level 100. A Super Shue will start from level 1 again after being bred. There is no level requirement to equip a Super Shue. An Identifier NPC can breed your 2 level 100 shues into a Super Shue.
Click on the Tab "Breed Shue" in Identifier window. Place two Level 100 Shues in the right slots in Breed Shue window and click "OK". The properties will be merged and a new "Super Shue" will be created. You can merge two different class Shues, eg a Warrior Shue and Mage Shue. Resultant Shue will be of the class of the Shue in bottom slot.