A few clarifications for those readers who are unsure how Omen Machine (and such similar effects instructing players to cast a card) works: When an effect instructs a player to cast a card ("if able"), and there is no word "may", that means that the player has no choice, and is forced to cast the card, if it can be legally cast
Shaman of the Pack is one of the best payoffs for running elves in formats like Pioneer
But up higher, where one instance of an ability produces a ton of Thran Dynamos and hence a ton of colorless mana, getting an additional copy for 2 mana is an absolute bargain
Enlightened Tutor This obvious choice for the deck can find most of the great cards in the deck
The Ultimate Box
Though this list is looking more at the flavour of the cards, it also fits really nicely with what the card does: you gain control of a creature in an opponent's hand, give it haste so it can hit its owner, and then callously sacrifice it at the end of the turn