how do you get ark as an eidilon?

i want ark to help me defeat necron!also i don't have all pieces yet but i found the shadow!!!

I don't know how much he does all the time but I used him on kuja once and he did about 6,293 damage so I said screw it and got reflect on all my characters so I could use a fira spell and do 9,999 damage(hellz yea)

I think Dagger is worthless but you dont need to beat ark with dagger IN your party... or at least i didnt.

Well you can use Dagger for healing purposes and if enemies are weak againest a certain element or if you use Curse on them you can use her summons (I always use her instead of Eiko.):D

I think the summons all suck at the end really. I just get em for the sceney bits. Yummy. Yeah anyhoo, you don't need Ark for Necron! You need characters that always hit 9999's (Freya, Amarant, Steiner, Zidane, Vivi and Quina are easiest) and healing's pretty pathetic anyway.