where's this skill at?

alright, so I'm going for this build A/D Critical Scythe Assassin, but I can't figure out where to find Critical Agility. the Wiki says it's a sunspear skill, but doesn't say beyond that where/how to get it.

Talk to a hero skill trainer. It'll cost you a hero skill point. Be sure to look under "Sunspear Skills" and not "Assassin Skills".

ah, thank you. I thought the hero skill could only be used by Heroes, not by the player :P