Jeskai Black has been all the rage in Standard lately, and many have made the comment that it feels like a Modern deck. Well, I'm glad someone finally tried to figure out how it would do in Modern!
Blastoids' deck is a minimalistic approach to a control deck, featuring basically the bare minimum amount of win conditions possible. Snapcaster Mage is going to have to do a lot of work here, but you should be able to clear the way with your plethora of removal. There are also some creature-lands and burn spells to help finish off opponents after your Snapcasters have softened them up a bit.
On the surface, this is a typical Jeskai Control deck, but Painful Truths finally gives the deck the hard card drawer that it has wanted for so long. It may seem painful, but Lightning Helix (and Snapcaster Mage on Lightning Helix) go a long way toward getting those life points back. Don't forget about Standard all-star Shambling Vent either, as that card is definitely Modern playable.
This deck doesn't do anything particularly well, but it doesn't have any particular weaknesses either. Removal helps against nearly every deck in Modern, and it has a bunch of built-in card advantage. The deck might lean on Painful Truths, but Supreme Verdict, Electrolyze, and Cryptic Command are also solid ways to pull ahead if you can't find a Painful Truths quite yet. I'm a tad surprised to not see any Lingering Souls hiding out in this decklist, but I can appreciate keeping the black splash to a minimum.
The sideboard is a mishmash of Modern's most powerful sideboard options, which is definitely something I like seeing in decks like these. Of these, Timely Reinforcements is probably the card I'm excited to see, especially considering its synergy with Painful Truths.