The typical midrange decks of Modern supplement their efficient disruption and two-drops with bigger, more powerful threats that can dominate a game by themselves. But what if that card already exists at two mana?
Young Pyromancer has been putting in work for years, mostly in blue decks, but this list certainly plays enough spells to get significant value from the card, especially if you clear the path for it with your many discard spells. Once you've generated three or so Elemental tokens from it, a topdecked removal spell isn't scary, since your own bevy of removal spells can clear your opponent's blockers, forcing your opponent to answer or lose to the tokens you got essentially for free.
Grim Lavamancer is a heady addition that supplements this plan by giving you another creature that can take advantage of the higher instant and sorcery count in the deck. It also lets your tokens trade up for any three-toughness creature, thereby giving you a significant advantage in attrition wars.
Lingering Souls solidifies the token plan as your primary means of applying pressure, thus making Sorin, Solemn Visitor an appealing addition. If your opponent doesn't have an effective means of answering your token horde, the game can end quickly, but even if they have some counterplay, this deck is more than capable of winning by inches.
For one, did you notice at first glance just how much burn is in this deck? Eleven of your spells go upstairs, along with Grim Lavamancer and Ajani Vengeant. Closing games from ten life is not unrealistic, making each extra point from Elemental tokens important. That amount of firepower means this list flips the script on Modern midrange decks, taking aggression as its primary plan and falling back on attrition.
Without knowing this, your opponents are likely to take poor lines and use their life total as a resource too liberally. This kind of subtle shift is very effective in Modern as we've all become so accustomed to the regular order of things, especially with midrange decks that have existed in more or less the same form for years.
And if your opponent mistakes you for some sort of burn deck, then Young Pyromancer, Dark Confidant, and Lingering Souls have some bad news for them: they're still dead. It's just that their corpse won't be burned beyond recognition. I guess they could take some solace in that, you know...if they were alive.