Who would be in your rivalry or what would be your rivalry. You could make more than one.
I would personally re-sign Gangrel and make him debut on ECW, and have him team up with Kane. After a couple weeks they would recruit The Boogeyman. Kevin Thorn would come back as the vampire and they would become the new brood. They would probably draw in heaps of ratings, and they would wreak havoc on people and "injure" Mike Adamle's throat so he could never talk again (kayfabe). I've never thought of an in depth storyline with this, but I would like to become a WWE writer because the storylines recently have been sucking.