Two Conclusions

"Well, that is true." Compass Carburettor nodded, gazing at the projection of the two worlds behind him, "This was also the reason I was kind of hoping to enter a battle of the mind. Since that was the best way to obtain my hand on this treasure before Regriel. And as I had expected, it is indeed a powerful treasure."

The ability to transfer bodies using Warble almost guaranteed immortality, as long as it wasn't destroyed. And, no matter the species it was implanted upon, the result would be the birth of a Haggon, the strongest Dungeon Monster with a whopping Darlac limit of 10,000.

So, the moment Regriel got his hands on the Warble, killing him would become stupendously difficult, if not straight-up impossible. He would be able to survive any situation as long as he removed his Warble and allowed one of his companions to run away with it.

It was the ability wielded by the protagonist—a System Host.