Hatebears has been a successful deck for years in many different flavors, from Modern to Legacy to Vintage. Using powerful creatures that can enter the battlefield cheaply and disrupt your opponent provide that combination many decks are looking for in aggression and disruption simultaneously.
Leonin Arbiter does serious work in Modern. There are lots of search abilities between fetchlands, Path to Exile, and countless other effects. Aven Mindcensor has a similar impact on the game, while Thalia, Guardian of Thraben slows down the opposition and makes the benefits of playing cheap spells in Modern much tougher to manage.
Stopping the opponent from casting their spells and search abilities is fantastic, as is the addition of further disruption. Path to Exile can turn into an improved Swords to Plowshares with an Arbiter or Mindcensor in play. Ghost Quarter turns into Strip Mine.
Flickerwisp is one of the most powerful creatures imaginable in conjunction with AEther Vial. An instant-speed creature that can target opposing permanents becomes an improved Restoration Angel. Protecting your creatures is great, and the addition of Athreos, God of Passage furthers that game plan—and a potential 5/4 indestructible threat when the game gets bogged down is another nice bonus.