Still in the search of it to complete my game at 100%. It cannot be high-level as on 3DS & Switch I've finished countless requests. I'm currently only using low-level miis, and I haven't seen it yet. I assume its between 25-35. i'll keep you updated on it tho.
All I need to 100% is to get 1 Grub & 7 Monsters including it (without the stupid medals : "1 Mii owns all Equipment & be Lv50 everywhere" & a normal Harpy encounter)
Refer to the Rank article to see the possible level range for it to spawn. Even then, it's all luck-based because there are other boss monsters and the quests given that day may or may not involve a "Traveler" monster at all.
Don't mention it. Credit to Armexploit for looking into the quest files and grouping the encounters based on those. The article was first made two months ago. It's still under construction from what I remember and the quest level tiering on the page actually doesn't reflect the one from the game code (in ranges of five (wiki) instead of three (game)).
Will it eventually get updated to make ranks of 3 levels instead then? If you guys want, if it gets done maybe ill add pics of the monsters & "tidy" it to not make it a huge mega list of unorganized monsters.