Known spawn location by the river:
Krondal has four levels of rage. After 25 seconds, he reaches the first rage level. 30 seconds later, the second. 35 seconds after that, the third. 40 seconds after that, the fourth. Each rage level is associated with a random spell-base (magic, poison, fire, or cold). In order to reset his rage back to zero, you have to cast a number of opposing spells on him (magic and poison oppose each other; fire and cold oppose each other). As rage levels increase, it will take more casts of the proper spell type to reset his health (7, 10, 12, 14).
For example: If, at his second rage level, he becomes associated with magic, you'll need to nuke him with poison 10 times in order to reset him back to zero.