Further Upgrades The first cards I'd pick up to further juice up the deck would be untapped mana-fixing lands: Watery Grave, Shipwreck Marsh, Underground River, Morphic Pool, Darkslick Shores, Polluted Delta, Sunken Ruins, Undercity Sewers, Urborg, Tomb of Yawgmoth and then maybe a couple more Island / Swamp fetches
That's simple enough provided your opponents obligingly block your vampires
Also, many of them have Enrage, which will provide a boon to you when they take damage
But when the card works, you get like a 10-for-1 because you cast two spells and obliterate opposing boards
Its still an awesome value creature though, so try to play a couple good ones for it to tutor
Likewise, Orchish Bowmasters is a great new black EDH staple that does the same kind of work here as Lotho, namely via punishing opponents who are trying to do too much by pinging any target and providing creature tokens that can end up doubled if you dont already have one