(If this creature has no +1/+1 counters on it, put two +1/+1 counters on it.) Permanents you control have Whenever one or more +1/+1 counters are put on this permanent, put an additional +1/+1 counter on it
Repeat this as many times as you like to draw your deck, setting you up for a Thassas Oracle win when your turn rolls around
And on the flip side, the idea that you could graft sliver abilities onto creature with bigger bodies takes my premise for Volrath, Shapestealer and cranks in up to eleven
While that's not the most terrible idea, the likelihood in a Niv-Mizzet deck is that the other spell you're casting is a burn spell that could do the same, and I have to feel that you're going to be better off casting it by itself, rather than putting all your eggs in one basket
The Nazgul would normally take up several slots, since most collectors value them all relatively equally and if you are running the card in a deck, youll likely want the whole collection