Here's a listing with pictures and lvls of all AI enemies and bosses. It says where they're located too but I can't read all of it though but it'll give you a good reference of who to fight. Plus it gives you how much health they have too.
http://www.aceonline.co.kr/guide/monster.asp
~Kill_Zone_
http://www.aceonline.co.kr/guide/monster.asp
~Kill_Zone_