Cetus, the Pelagic Jester -- a mighty phantom beast that dwells in the
Sea of Wonders just off Alexandria, and eagerly awaits challengers. Some helpful, nifty videos can be found here:
H-Gazi - Vs. Cetus: www.youtube.com/watch?v=RM5pBlwExos
H-Gazi - Solo Cetus: www.youtube.com/watch?v=AxIaea4FN1E
SuperGom - Solo Cetus: www.youtube.com/watch?v=hBpfpKmn-ww
Captain_Havok - 10 Tips and Tricks to Fighting Cetus: www.youtube.com/watch?v=RM5pBlwExos
Can potentially drop the following on defeat:
Cetus - 100% guaranteed to drop on your first victory. May drop again afterward, but the chance is very low.
Fish-like Phantom Monster's Relic x1 - high percentage of this item being dropped. However, it isn't 100% guaranteed.
Platinum Ore x2 - useful for many recipes, but it cannot be traded or sold/bazaared.
Red Ore x100 or
Green Ore x100 - YMMV on whether these drops can be considered good or insulting.
More information can be found in the comments on the Sea of Wonders page. Cheers.