>>58744943I went and did an attempt to give you a rough estimate of what to expect.
To the left you see the berries I had before going into the 4*.
Middle is the 4* I went to and what donut I used. Chose this one just because it had a Swamper that I hadn't caught yet, nothing else special about it.
To the right is how many berries I exited with.
In total, I got 110 berries in a single medium 4*. Discount the 8 I used beforehand to make the donut and that's still over 100 berries in a single attempt.
100% recommend this method.
