Over the years I've noticed that when you go into some of the older dungeons that don't see lots of activity, you'll notice a monster one second and then the next second, it has just vanished into thin air. Happened the other day when I went into Destard on one of the quieter shards (might have been Oceania). Saw a dragon sitting on the ledge by the entrance and thought to myself, "Aha, don't have to wander too far today to find a dragon to tame for my taming gain." Walked over to where it was, and it just vanished. I know sometimes those ledges in Destard can be kind of tricky for seeing stuff that's actually floating in the air, but this one had just poofed into thin air.
I've seen the same thing happen in other dungeons. First round of the morning to pick the locks on the chests by one of the arctic ogre lords in Ice, the OL's pacing around looking ready for a fight. Next time you pop in a bit later to pick freshly spawned chests, that dude's gone and a new one's way off in the corner. You didn't kill the first one, just danced around it a bit and got out. But when you come back, he's just gone. If you pulled his life bar, you can run around the entire dungeon and never see it light up again. And there's definitely no corpse on the ground or any sign that anyone else has been around. A corpse, if one has been created, would still be around by the time you made your next visit for picking chests. I've seen the same thing happen with poison eles and rotting corpses in other dungeons where I pick chests. The one you saw on your first round through just vanishes after a bit and is replaced by another one in a different location.
It's as if some monsters have a shelf life and an expiration date, but the game doesn't kick them into the recycle bin until a player comes along to trigger some kind of routine for checking the monster's expiration date.
Or so I tell myself, anyway.
