Well, Celans are know for 2 things:
Their reflect skill(s) and the Auras
There's 2 types of Auras: Blessing / Curse
For these, the person has to keep their character motionless to keep the skill running (20 yard range)
Then there's the reflect skill(s)
The major one is Moon in the Mirror, which practically reflects any skill (effects along with it) back at whoever casted it.
There's a few other skills that can give the reflect effect to the caster
Just to sum it up, they're really just the Athan version of a Skysong (heals, buffs single / group, resurrection, and group curses)
Oh, can use this to help ya a bit, just scroll over the skills and it'll say what it does:
http://jd.pwdatabase.com/pwi/calc/Celan#d