There are a couple directions I think Grixis can go in Pioneer.

One is a version meant to take advantage of the extremely powerful Draconic Roar, which I'm workshopping over at Grixis Dragons v2. Another is this hard control list, sort of a version of Legacy Grixis control in Pioneer - after all, everyone always says the real difference between Legacy and Modern is lands, and the real difference between Modern and Pioneer is lands, so it has to be good, right? The last and (in my opinion) most promising list, though, is this one - Eldrazi control specialized against combo.

So, why Grixis? And why Eldrazi? 

The Pioneer meta, for basically the entirety of the format's history, has been defined by combo decks. Dimir Inverter and Lotus Breach reign at the top of usage charts, and Spirits and delirium decks are the only real presence midrange and interaction have in the format. Despite some of the best disruption in Magic - Thoughtseize, Nimble Obstructionist, Silence, Kolaghan's Command, Tormod's Crypt - being legal in Pioneer, other than Spirits and its Spell Queller shenanigans, there's very little of that pressure/disruption mixture that takes down combo decks present in the meta.

However, I'm not so sure that this is because robust anti-combo control decks don't actually exist in the theoretical Pioneer deckbuilding space. Like I said, there are incredibly strong options for information, interaction, and disruption legal in the format (even if some are desperately in need of reprints), and I think Grixis control - specifically, Grixis control focusing on discard, pressure, hand manipulation, and multi-purpose answers - is actually in a really good position, and absolutely a playable enough one that it's really weird it has very little presence in Pioneer as it stands.

With the trio of removal, counterspells, and hand disruption shredding the combo-laden Pioneer metagame, what a Grixis deck really needs to be effective is some way to threaten the opponent's life total before they can rebuild from all its interaction. It seems to me that the best answer to that question is Eldrazi. Reality Smasher and Thought-Knot Seer have been two of the strongest midgame plays in Magic since their printing in Oath of the Gatewatch, Crypt of the Eternals is the only shard tri land legal in Pioneer and conveniently produces colorless mana for your big Eldrazi, and both Ashiok, Nightmare Weaver and Ashiok, Nightmare Muse are seriously threatening win conditions that meld seamlessly with the BFZ-era Eldrazi mechanics of exiling and processing cards. Ulamog's Nullifier transforms from weird jank into a tremendous tempo play in a deck like this, Sire of Stagnation becomes not an overlooked mythic but an absolute backbreaker, and Agonizing Remorse gets even better than it already is. Herald of Kozilek is available in our colors and really speeds up the deck's plan, and ramping out into Ugin, the Ineffable can mean game over. In addition, our beefy Eldrazi allow us to play the excellent Stubborn Denial, and Horribly Awry, Brutal Expulsion, and Warping Wail are all excellent utility spells made even better by what the rest of the deck has going on. Kolaghan's Command and Thoughtseize are classics for a reason, and they both help hold the list together in the early to midgame.

There are plenty of amazing sideboard options, too. Anger of the Gods, Bedevil, and Scorching Dragonfire are excellent here, Specter's Shriek is extremely strong against other black decks (including Inverter), and Mnemonic Betrayal, Unmoored Ego, and Ashiok, Dream Render are all terrific options against combo. Dreadbore would be more than welcome, but I kinda prefer Spell Pierce in the current meta (and it's always a great card). 

This is still a work in progress, but I'm really happy with it so far. I'd love some feedback!