Let us look more closely at the combo pieces.
Flash can be used to "discard" Raz or Jin if we have reanimation spell in hand, or convert an ETB creature such as Phyrexian Delver or Eternal Witness into an instant. It also can instant speed steal creatures to disrupt combos with Gilded Drake if we pay .
Protean Hulk: Hulk fuels Raz, helps assemble Food Chain combo with cards like Eternal Witness and Eternal Scourge, and serves as a wonderful decoy in our intuition piles.
Viscera Seer can be sacrificed for value and can kill Hulk. Its scry ability also comes in handy in a pinch.
Phyrexian Delver is a key part of Buried Alive pile and can win the game off Survival of the Fittest/Fauna Shaman activations. With a single creature in play and Entomb, Delver can win the game for 6 total mana. Delver also provides redundancy to Dread Return for Food Chain combo.
Phantasmal Image often copies a dork, bob, or ewit which is passable on its own. However, it can occasionally copy powerful creatures on the cheap and helps our Buried Alive pile be mana efficient.
Food Chain can help us ritual into Raz or Hulk or dig by exiling and recasting SBT for her mill trigger, but most of the time, this is just a combo piece
Eternal Scourge can be discarded to Survival of the Fittest, but is otherwise pure combo piece.
Mikaeus, the Unhallowed...Ditto
Laboratory Maniac can win with Tainted Pact giving us a gravefree victory that gets around hoser cards like Supression Field. Can also serve as a free backup win off Food Chain combo with Raz's help.
Tainted Pact can dig deep for cards we need to win. Since we have multiple win conditions, we almost always get a card we need without screwing ourselves and being instant and 2 mana, makes this card a very efficient enabler. If you got big balls you can even sometimes assemble both halves of food chain combo with this card (I do not suggest this).
Walking Ballista can be used to ping problematic creatures (i.e Hermit Druid) and is the primary win condition to both FC and Flash Hulk.
Lion's Eye Diamond has proven to be too powerful to pass up despite the fact it has less utility than Lotus Petal in non Razaketh situations (the card it replaced). LED lets us win off 3 creatures with Raz instead of 4, which matters a great deal when fighting through heavy disruption. For the budget conscious Tyrant, Lotus Petal is a fine alternative that is usually powerful enough to get us there.
While this deck has a number of combo peices, most have multiple functions, which reduces the negative impact they have on the deck.