Snapcaster Mage : Best blue card in Modern? An accident? Should have been red? Read enough forums and you'll hear these things said about Snapcaster Mage. For this deck he represents 2 for 1 card advantage, an instant speed blocker, instant speed reuse of your most relevant instant, synergy with Kolaghan's Command and an alternate win condition. He puts in major work every event and I struggle to see a scenario where I want fewer than the full play-set.
Vendilion Clique : This slot could go to a number of other creatures. Tasigur, the Golden Fang and Spellskite are in the conversation. I chose Vendilion Clique for the utility. It's a flash blocker with enough power to take down many creatures, can protect our combo with the ETB and is instant speed to allow us to continue operating on that axis. Like Snapcaster Mage, he can attack for the win in some games as well.
Deceiver Exarch : The Modern community has a lot of experience with this creature from its Splinter Twin days and it serves a similar purpose here. Ultimately, you want to EOT flash it in and then play Kiki-Jiki, Mirror Breaker on your turn for the win. Be aware of the utility Deceiver Exarch offers on top of being a combo piece. It's a fine flash blocker at 4 toughness, can tap down an attacker before combat, can upkeep tap an Eldrazi Temple to keep your Eldrazi opponent off of their big threat for another turn, can tap your opponent's last blue source to shut down their countermagic during your combo turn and lives through your own Anger of the Gods. Also don't forget that you can make plays on 3 mana like "flash in Deceiver Exarch, untap my Mountain, Lightning Bolt your guy".
Kiki-Jiki, Mirror Breaker : Our end-game goblin serves a much more narrow purpose than his friend Deceiver Exarch. A 2/2 at 5 cmc is a terrible rate, but he'll attack for 2 when you and your opponent have gone hellbent and it's all you have. He has some utility in the form of copying Snapcaster Mage or Fulminator Mage every turn if the game calls for it. Being so bad on its own, I tried 2 copies at first but felt like I didn't draw it enough despite the card draw and filtering so I bumped it up to 3 and have been much happier.