This is one of the few combo decks not running blue, which means there's not much hand sculpting or digging for pieces. This is overcome through redundancy. Loaded with 12 reanimation spells, 12 "discard spells" and 4 entomb, it's very likely any given hand will have multiple copies of the combo. This is necessary to both assemble the combo, but also play through counter-magic and hate.
INSTANTS and SORC.
Wear / Tear
Other considerations are towards a different game plan. There has been success with cards like Pack Rat, Bitterblossom, and more recently Rotting Regisaur. The rat and dinosaur provide an aggro plan, along with assisting in the overall discard to reanimation game plan. This approach has merit, as oftentimes opponents mulligan very aggressively towards hate, keeping otherwise weak hands.
Others have tried running a couple extra lands including Lake of the dead, in addition to a couple extra grave titan's. With the additional mana from Lake of the Dead, Grave Titan, and even Griesldaddy can be hard casted.
G-Daddy - The most common target. If a 7/7 Flying lifelinker isn't enough to win, sure drawing 7 cards, and bringing back another will do the trick.
Chancellor Of the Annex - This guy can win the game, but appearing in the opening hand oftentimes ensures a successful first reanimation. The tax on cantrips and everything else, often provides enough time to reanimate a second creature, or swing in for 20.
Tidespout Tyrant , Ashen Rider - Game 1 flexible answers to problem cards including Ensnaring Bridge, Jace, The Mind Sculptor, and Merit Lage
Grave Titan - A non legendary beefstick capable of singlehandedly winning games. The tokens provide reuse of cabal therapys to strip oppenents hand, and provides the fastest clock among the other targets. Can often out aggro tempo decks and even Death and Taxes.
Archetype of Endurance - Answer to targeted removal and bounce.
Inkwell Leviathan - Shrouded beat stick that can race most other decks with it's 7/11 trampling body.
Elesh Norn, Grand Cenobite - Provides a win condition, as well as a board wipe.
Iona, Shield of Emeria - Completely crushing card against mono colored decks. It also provides hate to things like storm, requiring that she first be removed from the field of play before they can win.
Sire Of Insanity - This was a popular option for awhile. Getting this bad boy out on turn 1 almost always spell game over. It's also a strong choice against decks like Show And Tell, or Storm as they usually require multiple pieces in their hand to win the game. Overtime it seems this may be a win-more card, and less valuable the later it hits the battlefield.
While listening to a mtg podcast, Eric Landon (one of the decks most successful pilots) mentioned his approach to the deck. He played it more akin to storm. On turn 1, if you have it, you might just have to go for it. But he also noted the merit to playing a little slower, and capitalizing on your opponents mana and situation. Making sure to lead with discard then comboing off with better information.