Lightning Bolt: The most played spell in Modern for a reason. Fits out game plan of clearing the way for creatures to sneak in and also helps us finish off the job by going to the face late. 10/10 would play 5 if we could.
Tarfire
: Extra copies of removal that happen to feed both Tarmogoyf and Bedlam Reveler. With lots of smaller creatures in the format right now in Affinity, Gruul Zoo, Abzan/Kiki Chord decks having extra copies of a 1-mana kill spell is great. Rarely does the 2 damage instead of 3 make much difference, especially in the earlier turns.
Flame Slash: We only need 1 copy of a 4 mana kill spell. A bit slow, but if we need to hit a Restoration Angel, Wall of Roots or any other random creatures we are able to.
Stubborn Denial: One of the best counterspells for our deck. With our plan to grow Tarmogoyf and Bedlam Reveler it acts as a 1 mana counter to every non-creature spell we can find due to the Ferocious ability. One of the more relevant counters across the format as well.
Gitaxian Probe: Some pros have called this spell one of the most powerful spells in any format due to the information you can gather. Checking to see if the coast is clear for a creature, finding out what deck they're playing in an unknown tournament or even just needing to trigger prowess on our creatures, this spell is very powerful. We often times will pay the mana cost for it as well.
Serum Visions: The card selection spell of choice, for Modern at least. We gain velocity through our deck, set up Delver of Secrets
to flip and can gain our incremental advantage over time. It's not ideal, but it's what we get. We need these to fuel our cheap Bedlam Revelers so we make do.
Dispel: People are going to cast their own Lightning Bolt and Path to Exile. We may as well keep them from killing our stuff. Also handy if someone thinks they're going to Collected Company or Chord of Calling for something cool. A big fat bowl of "nope."
Mana Leak: Only a 1 of and often gets sided out depending on the matchup. Plays well enough as a tempo play to keep the others from running away. As our only counterspell that hits creatures it fills a specific role.
Izzet Charm: A multipurpose tool in the deck. Helps us filter cards late with the loot effect, kill a creature early or a decent if underpowered counter. 1-2 copies in the 75 are always going to be appreciated due to the quality of each mode.
Seal of Fire: As a 1-of it does a few things that we really can take advantage of. One in being cast to sit on the board as a "free," Shock later. Two in we can cast it and leave it around so we don't have to discard it to Bedlam Reveler's ETB effect. Finally, it's another spell that we can use to pump Tarmogoyf proactively in any matchup.
Spell Snare: In Modern turn 2 plays are SUPER vital to furthering game plans. Whether you hit someone else's Tarmogoyf, Voice of Resurgence or any of the large amount of 2 mana kill spells it will have a target in 99% of our games.
Traverse the Ulvenwald: Such a crazy good card. Delirium is nearly a given in our deck, sometimes as early as turn 2 or 3, so it gets to act as extra copies of our Bedlam Reveler or Tarmogoyf late game. This card card be absolutely backbreaking against the control decks of the format, especially in sideboard games.
Echoing Truth: The final card in our toolbox-y build. Sometimes you just need to bounce a pesky artifact or planeswalker. This fits the bill. Against Elspeth, Sun's Champion or Lingering Souls tokens it can clear some major real estate and set the opponent back several turns.