The first form is easy.
The problem with the second is that it is continuosly casting Imprisionment.
Here is what my solo assassin/fighter done:
1 - Get out of Kangaxx range of view.
2 - Equip your character with Ras and Staff of the Rynn
3 - Cast symulacrum (Helm of Balduran)
4 - Summon Ras with one of them
5 - Attack with Ras
6 - Attack with both characters with Staff of the Rynn
7 - When Kangaxx becomes injured, summon Ras another time with the other character
8 - Attack with Ras
9 - Attack with both characters with Staff of the Rynn
10 - Just beat it to dead