This boss is included in the ''Resurrection of Goblin King Party Quest''.
Using the Mirror of dimension
Go to ''resurrection of hoblin king"
Form a party, minimum 3 party members.
Go in the PQ, protect shammos, he will be walking through 5 maps, you will need to protect him in order to get to the Rex boss map.
Map: Ice ravine 1, 2, 3, 4 and 5.
Rex boss inside ice ravine 5th map cave.
