How to Evolve Sinistea in Pokemon Scarlet

To evolve your Sinistea into Polteageist in Pokemon Scarlet, you need a special item called the Cracked Pot or the Chipped Pot, depending on whether your Sinistea is a Phony or Authentic form. First, find out which form you've got by checking its underside in the summary screen. Phony Sinistea evolves with a Cracked Pot, while Authentic Sinistea needs a Chipped Pot. You can find these pots by exploring the world, winning them in battles, or purchasing them at Delibird Presents shops in various towns.

Had a Sinistea that wouldn't evolve forever until I discovered it was the wrong pot! Make sure you're using a Cracked Pot for Phony ones and a Chipped Pot for Authentic. It's all in the details, folks.