Yrden is the first sign on the list in The Witcher 3: Wild Hunt and it is a surprisingly useful one although it doesn’t always seem that way. The Yrden sign is a magic trap that is cast on the ground and takes up a relatively large circle around the point where Geralt is standing at the moment of casting. Once an enemy steps into the circle, that enemy receives a drastic loss of speed, and in some cases (like with certain wraiths) becomes vulnerable to physical attacks.
This Sign is perfect when dealing with several quick-footed melee fighters at once. Geralt of Rivia can dance around with the best of them, but even he has his limits, so slowing things down allows players to adjust and catch a much needed breather. The Witcher 3: Wild Hunt will also throw spectral opponents at Geralt every now and then, and in those cases the Yrden sign is absolutely necessary. Anything that steps into the circle loses its magical defense on top of being slowed.
So, when neither one of your swords seems to be cut out for the job, cast the Yrden sign and take control of the battlefield.