2x Kalitas, Traitor of Ghet is one of the lower mana cards in the deck i would classify as a threat. Although he isn't huge on his own, this vampire has a lot going for him. Lifelink is great on him, as it gives us much needed relief when we're dealing with super fast aggro. His second and third ability are also great. This deck has tons of removal, so we have lots of opportunities to get value out of it, and before long have a massive zombie swarm. We can then sack zombies so we gain even more life off Kalitas. One thing to note is the tokens off of Return are zombies, so Kalitas can eat them as well.
2x Chandra, Torch of Defiance is one of the two planeswalkers in the mainboard of this deck. She hasn't seen quite the level of play some expected she would, but Chandra ToD is still a great card. Her first +1 is great for this deck lategame, as it prevent us from running out of steam. In the worst case scenario, she exiles a land or something we can't cast, but then we get in free damage. The other +1 is used only in fringe situations, but it sometimes allows us to drop an additional threat or removal spell in a turn. Her -3, like Cut, kills most relevant threats in standard. I'd prefer not to use Chandra's -3 if i can, as I'd like to keep ticking up her loyalty to threaten our opponent with the ult, the -3 is a great tool for when you have no removal in hand and need to kill something so that you or Chandra won't die. The -7, finally, basically auto-wins the game. And at only 4 turns away, it's not completely unreachable. In grindier matchups, especially those where our opponent doesn't have the means to deal with a planeswalker, this can easily win games. However, it's not quiiite an autowin like some other ults, as if we're super low, and don't draw enough spells, our opponent can still smash through a bit more and win. Still, Chandra ToD is a great card for this deck.
4x Goblin Dark-Dwellers is basically Torrential Gearhulk lite. It loses the flash and can only cast spells 3 or less, but it more than makes up for it with evasion and a cheaper cost, and the fact that this deck has no spells that cost more than 3 anyway. The Dark Dwellers are typically used to flash back removal, getting us way ahead on board, not only with a massive body, but by replacing itself. Menace is a great evasion ability, as this deck kills so many creatures our opponent will rarely have enough to block these Goblins. Finally, Sweltering Suns is great with this dude, as it lets us clear the board of all small creatures while leaving him alive. Just be wary that your opponent may have Magma Spray and be able to kill the Dwellers if you do so.
3x Glorybringer is actually quite similar to the Goblins in this deck. Both come down around t5, and typically trade with a creature while doing so. The Glorybringer's effect doesn't trigger on ETB, meaning that if he gets hit with removal instantly, we don't get much value out of him. However, haste and flying makes him both faster than the goblins and sometimes harder to block. He also has to attack to get any value out of his ability, meaning you can't leave him as a blocker and still kill something, but he makes up for that too by his effect being repeatable. All in all, I like him about as much as the Goblins in this deck, but run 1 less Glorybringer because of the Goblins versatility in being able to bring back different types of removal.
2x Ob Nixilis Reignited is another fantastic planeswalker, who is similar to Chandra ToD in many ways. His +1 constantly refills our hand, although the life loss can be somewhat irritating in games where we are behind. Ob Nixilis's -3, similarly to Chandra's, is a removal spell. However, Ob Nixilis gets an unconditional removal spell, allowing him to get rid of some creatures this deck struggles with. Finally, his ult, like Chandra's ult, is very good, is reachable, and can do a lot of damage, but is not quite gamewinning. Again, Ob Nixilis is great for grindy matchups, but can provide removal in faster matchups.
2x Combustible Gearhulk straight up wins games. 6 mana for a 6/6 with first strike is already crazy. There's very few cards in the standard meta that can trade with this guy, most will just die or survive but not kill him, besides Rhonas the Indomitable and Verdurous Gearhulk. His ability is what makes the card though. Sure, our opponent does get a choice between a ridiculous amount of damage and a ridiculous amount of card advantage, but we're normally happy either way. Because of the expensive threats in this deck, it's pretty common to get around 6-7 damage of this dude, which is certainly not too shabby at all.
