I've talked about Migi pens once before, in my Saran Wrap Spiderwebs manicure. If you're unfamiliar with how they work, the pens arrive in dual ended sticks, but each end can be disconnected. I would recommend keeping them together though as the added length of the stick can make it easier to draw! The pen caps can be unscrewed to reveal a normal nail polish brush, or you can leave the cap in and use the metal nib to draw as you squeeze the body of the bottle.
The doodly shapes are so colorful and cheery, they remind me of kindergarten doodles or an 80's print or something. I think I could still use a bit of practice but all in all a pleasant experience!
Visit the Migi Nail Art Pen website here and their online shop here. I purchased mine on Amazon -- the set I ordered is called "Beautifully Bold" there and appears to be called set #101 on the Migi website.