I dont want to miss any trainers in any worlds but the only one i found in the tree worlds stated is the one that gives the minion trade-off spells. So are there any other trainers in MB, MS, or DS ( note: dont post about WC or KT trainers i know them all )
I am also wondering about MooShu and Dragonspyre, but I found the trainer in Marleybone. He is in Digmoore Station. Behind the mayor is a staircase that leads down to a door. Go inside and you will find a trainer.