User blog comment:BannedLagiacrus/Monster Appreciation Week: Leshen and Ancient Leshen/@comment-4370375-20190830190153/@comment-24734669-20190830215144

"Jhen Mohran, Dalamadur, Gogmazios and Nakarkos were all introduced as multiplayer exclusives with only Jhen getting an offline scaled quest."

The difference between all those monsters and Ancient Leshen is that the former aren't as durable as a planet.