Nightfall skills

I was looking into different builds for my assasin and I found the skill Critical Agility. Now, I created my character in Factions but have been playing in nightfall. I was trying to find this skill to add on as I have hero skill points. but I can't find it. I tried the skill trainer in sunspear great hall and the sunspear sanctuary. I am a sunspear general. So I have no idea why I cant get this skill. How do I unlock it?\

Never mind figured it out

It is a Sunspear based skill so you have to have to be a certain Sunspear level to learn the skill from Pikin(Kamadan), Shiloh(Sunspear Great Hall), or Libeh(Command post).

I think it should be in sunspear great hall, but go try kamadan since I know it is there. The skill is under "Sunspear Skills" not "Assassin Skills". I don't think there is a minimum rank, you just need at least 1 hero skill point. Make sure you are going to the hero skill trainer, not the normal one. Yes its odd that the only skills a hero can't use in the game are at the hero skill trainers.