Then take ghost instead of Tele, I am just a tele person, Boots of swiftness add a good deal of speed, and 82 dmg every 3 or less sec is awesome. Not to mention the rylai's is giving out slow, and the idea of morde is to gank, so you should have stuns/slows with you. The morde ulti/ignite combo deals good DoT no matter your build but the spamming Siphon is your biggest spell besides IMO. It does most of your work (creep kills/passive sheild/dmg)

Like I said, it's unusual build, but I saw it get used perfectly, and I've been in love with ever since.

Oh and btw, read his ulti description.. AP has a good deal to do with it (does 4.4% of HP in dmg) which .4% can be handy late game, and you'll gain get more AP due to it. If morde's ghost wasn't rigged enough, it now has plus 200+(25% of target AP) HP/AD/AP
I also use creeping death effectively for creeping and the creeping death/sunfire combo it hands out good damage as well. AP gives it some more (15%)

And I did change the items a bit, kind of forgot how I did it. That's more accurate though.

Interesting idea but since only one of your spammable abilities scales off of AP and its only 40% that is only an extra 82 damage which I don't see doing enough damage. On the other hand your team is playing well (which it won't) then your ghost is going to hit for a lot but since it can't CC its really easy to run from and I don't think its going to be able to kill someone before they run away.

Lol very interesting.. I have an urge to try it.