Back to the FFR card for Den-O to become Momotaros, Kaito needed Momo to accept his fate in becoming Denliner. If Diend possesses every Rider card, then why couldn't he simply summon Den-O and FFR him into Denliner? Does he not possess a Den-O card, or do certain FFR's require the World's Rider and not a summoned one. This wouldn't appear to be the case as Diend has already summoned and used the Kivat Bow and the Blade Blade. I like the idea that Diend can only summon dead Riders - it makes a lot more sense to his name. The only differences between Kiva and Blade are that Wataru was half Fangire and Kenzaki became a Joker Undead. So could Diend only summon Riders who are dead or not human? The only exception I can think of to this is in the Cho Den-O movie where Diend summons G3 - I cannot recall any G3 user dying or not human.