It's an interesting system...
A friend and I played around with it a bit earlier. She was on rdm, I was on blu. We went to east ronfaure and popped some mobs for a while. Quagmire Pugil and Sunderclaw (crab) showed up every time. We were able to duo them just fine, they weren't too tough (though not easy).
We got ~200xp per fight, which was actually kinda cool for things we could duo like that. Getting up to chain 3 or so, we were enjoying the exp. Magic seemed to work well on them, too, which was nice. Was thinking it was a cool exp idea. Then my key item upgraded to the colored abyssite.
The next mob we found was Capricornus, a gnarly looking pugil who is just mean as all hell. Seriously, that thing sucks. Was hitting me for 300-350 per hit on my blu when shadows dropped (which happened a lot due to the lousy pugil attack rate).
Also, after a bit, it popped mighty strikes and used it's Recoil Dive move (which takes all 3 shadows, like a super upgraded screwdriver) for about 800 dmg a pop. It used it 5 times in a row. We wiped on the 5th, dunno how many more it woulda done.
We tried it again, buffing up this time, and it was no better. The thing seems to have some finicky hate issue. It liked to take off after her when she barely did anything to it and I was unloading damage on it.
We also learned that it seems to be able to throw out it's 2 hour when it feels like it, since it did it a few times. And that Recoil Dive thing is a *****... he slams everyone in sight.
Anyway, we couldn't get past him, and saw a party of 7 have some issues with it, but finally kill it.
Saw one other mob, a Sea Monk NM... Yacu... something. It's also in ronfaure, and also mean.
Seems to be a tiered set up. Kill enough monsters, upgrade your abyssite for finding stronger ones. Lather, rinse, repeat.
I do like the idea of it, though. Monsters just past our dimension wandering around, and using the key item and resting to pull them through.
Resting with the key item, though, is a bit dangerous. You can get unlucky and rest right on a mob by accident... as we found out.