Displacer Beast allows you to venture into Dungeon repeated times
If youre running decks that have big creatures, it can be pretty impactful and help you close out games
Players will still likely see Lurrus played after the change, since its ability to cast cheap spells from your graveyard is too good to pass up
Timed right, that can be a massive game changer
The most common pairing is Numa, Joraga Chieftain, but I prefer Thrasios, Triton Hero (one of Magic's best merfolks) or Tana, the Bloodsower for a better color identity
Oops All Spells was the final nail in the coffin for Simian Spirit Guide, as it was routinely able to win the game on turn two or three