http://www.phantasystaronline.net/forum/index.php/topic/12414-ultima-summer-event-2014/page-1
http://www.phantasystaronline.net/forum/index.php/topic/22788-ultima-summer-event-2015/
The follow has been made up from posts on the above link. If players post information below as they find it, I'll try to update the main post as it goes. As a noob I have no idea what half of this means, its mostly just a copy/paste quick reference. Information initially combined from data over the last 2 years (which differ somewhat). So as you get me right, I'll get it right. Take the 'drop rates' with a grain of salt.
Epsilon, drops item 1/3d of the time. *3 for accurate drop rates.
Epsilon + pinkal = bad??
Epilson + blue = good??
Cent/battle: (C\ B )
Falz Purple 1/102
Falz White 1/102
Epsilon Skyly 1/102
Kondriu Oran 1/205
Girtabuble Yellowboze 1/73
Psycho Black Crystal (PBC):
Morfos Redria 1/73 Ultimate
Morfos Bluefall 1/73
Morfos yellow 1/73
Blood Sword:
Saint million Pink 1/9
Saint million Purple 1/9 Ultimate
Trap/search:
Garanz Viridia 7/32 Ultimate
Garanz Greenhill 7/32
Baranz
Soul Booster:
Gibbles Redria
Gibbles Viridia Ultimate
Gibbles Oran
Zanbeacon:
Hildebear Viridia Very Hard
FOREST Very Hard
FOREST Skyly Ult (Good drop rates)