Some ideas:

Tolaria West + Pact of Negation: protection for your insta-win

Remand: TEMPO!

Muddle the Mixture: counter or tutor for your Heartless Summoning/Myr Retriever

Myr Superion: 4/5 for no mana with Heartless Summoning in play.

@Uskebasi Pact of Negation and Remand are two counterspells that don't do enough for the deck. I'm currently working on a second version of this deck, and it will be using Spell Pierce. Its cheap enough that we can survive early game, without the potential dying from Pact of Negation.

Muddle the Mixture is just too slow to be a combo. I've tested it, but just digging for more cards works better than tutors and allows us to have faster victories. This is a gimmick deck, so we need to combo off before other decks can establish a board presence.

Myr Superion is one that I go back and forth on. It's excellent to stop aggro and such, but it is a dead card if I don't find a Heartless Summoning. Depending on how my deck fares against different aggro decks, I may have to add this one in. I just finished this deck on paper, so I just need to playtest it extensively.

Thanks for your suggestions!

Sleight of Hand to more digging?

@Uskebasi That is another one that I am stuck between. Sleight of Hand helps get our combo online faster, but Gitaxian Probe is free and also can be used to assess if there is countermagic or other threats. I will likely stick to the Gitaxian Probes, just because they can be played for free and allow me to guarantee that my Heartless Summoning can hit the board.

I know this was said before, but I think Blood Artist could be a possible addition/ win con.

Ignore previous comment I feel dumb :/

So I added in a new potential sideboard. Anyone care to comment on the changes?

If you are milling, Surgical Extraction is always a great choice for removing key combo pieces.

Noxious Revival can also be used to lock down the opponent's next draw, or reuse something you want.

@Milkaholic The milling will typically be insignificant unless I am going infinite, or they are trying to use scry to their advantage. I would rather not devote my maindeck or sideboard slots to unnecessary cards that don't protect the combo or speed it up. Thanks for the comment though

Would it make sence to put Academy Ruins in your deck as a way to get artifacts back ?

@Dre4mc4tcher Sadly Academy Ruins is a bit too slow. Typically I try to combo off on turns 2-4, and I don't have the space in the deck for the colorless mana or the tapping three lands for a single card. I see Academy Ruins as more of a EDH card.

Hmm. Great idea. Love the thought of a transform sideboard in modern. +1

The maybe board sideboard seems like a great idea, especially against controls that will tune there decks post round 1 to hate on your combo. Plus a free 5/6 is just brilliant. Fantastic deck, though it does suffer a tad from the banning of Dig Through Time, though believe me, I know the feels. Either way +1

Yeah, I'm sad that Dig Through Time was banned. Mulldrifter is kinda decent, it lets me from 3 cards for , so it is decent. Also I like the sideboard, but it isn't always as good as the Spell Pierces and Inquisition of Kozileks for control matchups. I'm undecided on which would be better to play.

Anyways, thank you for the +1

To be honest I'd rather run Spell Pierces, as it can save your hide. Yes seize effects can preemptively remove a threat, but pierces can more than often stop things that would shut down your combo in their tracks. Another card to consider is Dispel, though it usually is better as a sb card.

Well, the main reason why there are Semblance Anvils in the maybeboard is to ensure that at least one piece resolves and we can start cheating out things.

Dispel is a pretty good card, but typically this deck is fast and Spell Pierce is enough. I'll also take the versatility of being able to hit Splinter Twin and such if I need to.

How did this do in a modern tourney mine has a couple of mind grinds and cacking counterparts and mana leaks and condescends and some mind sculpts ! Not posted on here

It does fairly well unless they have a lot of mainboard counterspells, the only really bad matchups are against Scapeshift and Affinity. Although we can sometimes outrace Affinity. I have about a 60% win ratio, not idea but still good for the amount of budget that I invested into this.

Also it sounds like your deck is much more mana intensive and mill based. This one is 100% combo based.

thought of myrq during the day so...

+1

I'm not 100% sure what myrq was supposed to say, but I'll happily take the +1. Glad you liked the deck.

I feel like putting in a couple Disciple of the Vault, or even Blood Artist could make this deck crazy. Infinite life loss with Heartless Summoning and two Myr Retriever, or Havengul Lich and Myr Moonvessel, and with Eldrazi around, mill may not always work without a Rest in Peace.

I just realized, those guys die to the summoning, so never mind, haha!

But you could do Falkenrath Noble

Falkenrath Noble is kind of cool, but it is also really slow. I use Altar of the Brood as a wincon since I can cast it for free while comboing off using Myr Moonvessel. However, I would need open to cast Falkenrath Noble, so it would often happen where I would need to wait a turn to play it. I've designed my deck to be 100% combo oriented, so speed is essential.

Thanks for the comments though. I really wish that Blood Artist or Disciple of the Vault had 1 more toughness

Nice version! Take a look to my Which Combo Do You Want?