u can get an arcadia when you fight pringer the second time, or the third time when there are 8 making it easier for a legendary arcadiaia to come up. --- im a random poster. http://img34.imageshack.us/img34/2553/75926407.png
This is off the top of my head, but I think it's stolen from a unit in the last X-Dimension stage.
Claiomh Solais Overlord Suit Aegies Shield Exodus
Each one is around Level 1200 and you're basically limited to front stealing so you'll need around a level of 1325 for a 99% Steal (1400 if you're aiming for Legendary Rarity 0). Assuming you're using a Bandit's Hand, anyway (50 HIT). --- Imagine I said something witty or profound here.