NiGHTS into dreams...

I originally thought this achievement was stupidly hard, considering I'm new to this game, but after some practice I came up with a method that worked for me.

I found that if you wait about 2.5 seconds at the beginning, then following his tail about half way down and then paralooping clockwise back on yourself, I was getting 17/19 link pretty often; eventually I hit the needed 21 link.

I've uploaded a video of said method in action, too.

This might not work for everyone, but I thought I'd throw it out there anyway. Good luck!

For those unfamiliar with NiGHTS terminology, a paraloop is when NiGHTS catches the shining trail you leave behind as you move. This is most easily achieved by moving in a tight circle. Gillwing is the boss for the Spring Valley level (the first in Claris' story). As the description states, you need to paraloop Gillwing's tail. This is easier said than done. I'm including the video that I found on Youtube which gave me some sense of what I needed to do, but it moves so quick that I'm going to give some much needed explanation. Gillwing flies around the area, slowly alternating from up to down halfway around. You want to position yourself where Gillwing will be traveling up, anticipating where the END of his tail will be. Your paraloop needs to catch his tail toward the back section. You will know you are successful when you get 21 Link. Through trial and error you can establish the exact position you need to paraloop based on how close the number is to 21. As a side note, I highly recommend beating the level first before you attempt this. When on the level select screen, you can press X over any level you've beaten to play that level's boss. Accessing the boss this way allows you to restart the boss quickly and efficiently, should you mess up. Good luck!

Credit to MilesSMB. Without your video, I had no idea this was possible.