After the 4th and final try, I am content with the results.

The first two times I struggled with the stranding, at which I am just no good.

Then the leaves gave me some trouble, but I finally figured it out. Doing the leaves correctly essentially amounts to performing the K2tog decrease stitches one stitch earlier than a ‘normal’ hat decrease - in other words, decrease row 1 should read: K2tog, K6 around until you get to the last 8 stitches:K2tog, K5. You will have one stitch left before the marker - knit this stitch together with the first stitch after the marker. Repeat this sequence around each time ending the round by knitting one less stitch than you had been, always ending up with one extra stitch to be knit together with the stitch after the marker. Continue in this way until you have 4 stitches left and make your I-cord.