Why ITH's?

Going to lvl my Hc sorc to 99 currently 94 and going to use Arkaines, Valkyrie wing and Cliffhanger so i'll see what it get's with 6+ in skills, when it has 5 it shoots a poison thingi from poison nova, very lame indeed and i need to use 1 fal rune in valkyrie and cliffhanger so merc has enough strenght >.<