[@vancexentan]
Talking about Rider's NPs, I would have his Noble Phantasms being a Reality Marble that essentially 'draws in the tide of the ocean' and over a series of turn will eventually create an ocean if not stopped. Outside of simply flooding the area, it does little else than that unless used with his other Noble Phantasm. 

I won't lie that I stole this from PotC (Pirates of the Carribean) but then summon the Flying Dutchman as an 'ace' up Rider's sleeve. Both the two represent the major folktales of tragedies from the seas and I would hoping to incorporate the two if it was possible. If not then its perfectly fine but I'll have to change some things! 

(As for being the master of Caster, I will offer taking them as a master as well if no one else wants it.)