I had initially meant it to be Chall's natural magic, but if it suits something else, feel free to make it that. That is the great thing about working with someone else, sometimes one's ideas get turned on their heads. :) He might be going after a spell someone put on him, or perhaps he's capturing Chall's actual essence, or ... who knows? I see him as very ancient and very powerful and luckily, not overly interested in people. Kind of like maybe this pond had been a druidic sacrificial hollow complete with stone alter or something. Or maybe he's just the embodiment of the old magics and there's been enough care taken in this town that it remains strong enough to actually gain a body when the spirits of the pond over-drain Chall. 

I am really quite open to any way you wish to interpret it all. If I'd had a very set idea, I'd have told you so you could work around it, but I rarely get too set in my ideas when RPing because I've had that shifted under me often enough that I find it somewhat naive to try and direct everything when I'm co-creating as opposed to GMing or some such.