I'm horrible at building sideboards, but I'm pretty happy where this one landed. Obviously, make changes as you need to fit your meta.
Engineered Explosives - This card is so versatile, but the main reason it's here is to kill Rhinos, Dragon's Rage Channelers, Ragavan, Nible Pilferers and Colossus Hammers. Yes it kills our constructs, but when you control it it's easy enough to play around, and the match-ups where it's good, it's sooooo good.
Tormod's Crypt - Another graveyard hate card, mainly for specifically Living End or Dredge, maybe Izzet Tempo.
Grafdigger's Cage - Just a good card to have access to. Does shut off our Emry, Lurker of the Lochs, but I think it's worth it.
Pithing Needle - This card has so much application, and can help us win matches we would otherwise struggle with in game 1. Turning off Planeswalkers, or certain creatures, it's just an extremely useful card. The opportunity cost of running 1 was just too tempting for me to cut, although it could be moved to the sideboard, as it has it's fair chare of dead matchups.
Ceremonious Rejection - Couldn't find much room for Tron hate, so I guess it's something! Likely the only match-up where this comes in, but I don't want to be entirely dead to Tron.
Fatal Push - Efficient removal for those pesky aggro decks.
Flusterstorm - Good for the cascade decks, as a 1 mana counter that they can't Force of Negation back, and helps resolve important spells against control. Overall just a very powerful one mana spell.
Aether Gust - Might take this one out, as it seems narrow and slow for the current meta, but one copy seems fine to me. Seems pretty good against Fury and Crashing Footfalls, so it's probably worth a slot.
Metallic Rebuke - Cheap counter magic for when we need it. Can be held up on turn 2 for 1 mana a lot of the time, so I think it's worth it. Only time will tell though.
Ashiok, Dream Render - Graveyard hoser that also hits the Amulet of Vigor decks if you can get it down early. Figured one is worth to have for sure, might need to find space for a second if it performs well.
Tezzeret, Agent of Bolas - Ok, this one is probably not good enough, but Tezz is one of my favourite cards of all time, so I couldn't help but put 1 in the 75. Seems fine against control if you can resolve it I guess, especially because it dodges most Prismatic Endings.