You suggest killing him with the guards-I did it twice after getting him halfway down on my own, BUT you are NOT allowed to loot, therefore making this solo at 27 not do-able.
Also-when I put a red “X” on that part of guide, Both Tidress #21 and Ursangous #24 got red “x’s” next to their names. I had un-check the red x’s from both of them-buggy.
That is because the character must do enough damage to the mob in order to get awarded the kill. It is just too early to do this quest IMHO. I suggest you hold off on it, and come back in a level or two. ‘X’ the quest and come back, perhaps.