Attached I-cord is one of those things which are probably harder to explain than to actually do! But let me try - pick up the stitches of your provisional cast on (a circ is probably better to do this). Slide these stitches down so the first stitch is near the end which you will start working from. With a dpn cast on 4 stitches for the I-cord. Knit across these (with another dpn) to the last stitch and knit this last stitch together with the first stitch on your circ. Pulling the yarn behind the I-cord (just as when working a normal I-cord) knit the stitches of the cord until the last stitch and knit this together with the next stitch on the circ. Repeat until all the stitches on the circ have been worked. Cast off the four I-cord stitches.
I know it sounds complicated but it really isn't when you try it! I would suggest doing a small sample and trying this method first before tackling your Mermaid! Just remember that if you use this method you do not need to do this at the very beginning. It will be easier to do it after you have knitted several inches of Mermaid - if not at the very end! Happy knitting!
KathyR Rudeness is the weak man's imitation of strength.