Gauge is not all that important. You want nice tight stitches to keep the stuffing in, but not too tight or the toys become stiff and difficult to work. Feel free to use larger or smaller hooks to make larger or smaller oddishes. Maybe even split the ply of your yarn to make tiny oddishes, or double it up for bigger ones.

Also, you will need pink yarn or fabric paint to create the eyes and mouth.

I’m not sure how many yards were used for each oddish, but one ball each green and purple yarn easily made 12 oddishes.

If you’d like the leaves to stand up better (and make them pose-able) you could work the the non-slip stitches over a green pipe cleaner or jewelry wire.