What cards should you have in your sideboard (or even main deck) to have a chance in our current fast and broken Modern format
While it does change the power and toughness to 1 for the creature you target, you might not be going to win through combat damage anyway depending on your build
The simplest answer is graveyard hate, with cards like Leyline of the Void, Rest in Peace, and Relic of Progenitus being among the best in the format at fighting Dredge and Surgical Extraction also offering a decent amount of value if you can get the timing right (exiling Narcomoeba or Bloodghast makes it hard for Prized Amalgam to return to the battlefield, while getting rid of Creeping Chill with the "exile" trigger on the stack will fizzle the damage)
Mardu Energy excels at flipping Sephiroth in mildly impressive boards, turning into an easy win condition that can double as card generation
Shards of Alara , the first set in the block, was fundamentally about five shards, that is, five parts of the plane that broke away from the rest