"Charge!"

Opening his mouth, Alexander let out a pulse of mana, which acted as echolocation, and it all became clear as day to him.

In the tunnel under him, trying to strike at his underside as he blasted past them, nine out of ten enemies appeared to his mana vision as almost translucent. Their bodies were barely sending back an echo as the mana had to traverse a liquid-like state, barely bouncing back.

And there, at last, he found it: the elusive source of the magic phenomenon.

Far behind the kobold tide, two different creatures stood, their mouths open as a soft melody escaped their lungs.

Two lanky harpies were chained to larger kobolds, their necks and hands held by heavy manacles, as they sang a magical tune.

The tune washed over the advancing kobolds, which went from one kobold to a unit of ten or twelve, all bearing more than just a passing resemblance to each other.