As you progress through Pokemon Sword & Shield you’ll come across a lot of odd items that may seem useless. Most of the time, these objects are used to either improve or evolve certain Pokemon. One of these is the Cracked Pot, which automatically evolves your Sinistea into Polteagiest. This Ghost-Type Pokemon is new to the series and cannot be evolved by increasing its level via earning experience.
To find the Cracked Pot, head to Stow-on-Side (the fourth gym) and stop at the marketplace near the base of the stairs. Speak to the man standing on the right to initiate a dialogue exchange. This gentleman sells daily bargain items, one of which is the Cracked Pot. If he isn’t selling the Cracked Pot, you’ll need to keep visiting him daily until he has the item. Remember, you can always ask him what tomorrow’s bargain item will be, so you know ahead of time.
Alternatively, run up the stairs towards the stadium and take the first ladder that appears on your right. Climb on top of the roof and interact with the Pokeball on the ground to obtain the Cracked Pot. You can see the location in the video above by Youtuber JohnnyCanal.
Once you have the Cracked Pot, open up your menu and put Sinistea into your party. Now go over to the Other Items tab in your bag and select the Cracked Pot. Using this item on Sinistea will instantly evolve it into its final form.