Is it the duelist that spawns randomly in the duel world, or the one found at the duel gates? (For reference im attempting to get ojama blue)
Whenever you duel a standard duelist or legendary duelist, his level is always mentioned.
Level 40 should be legendary duelist.
legendary duelists could spawn in duel world in lv10,20,30 or 40.
To make sure you get a lv40 you can always spend keys at the duel gates.