Folio of fancies use some mana to make the draw thing, yes, but also give you the option to win by milling, because players have no maximum hand size and you are making both players draw many cards and it's different than creature type, so opponent need to deal with artifact and creatures, not just one thing. That gives you more chances to get mana and play them every turn, so the CMC of Ob Nixilis isn't that much. Also if you get more than 1 Folio, you could mill the opponent very quickly.
Rankle, Master of Pranks is pretty nice too as Rooker saids.