Although an unusual creature Yin-Yarn is nevertheless incredibly powerful and split the realm of Patch Land into seven parts while also causing chaos in both Patch Land and Dream Land via transforming people into yarn and creating many yarn monsters in order to prevent Kirby from undoing his evil alterations of reality.
Yin-Yarn sought to conquer the universe (or at the very least Patch Land and Dream Land) - wasting no time in manipulating and abusing others in order to do so, he was also a powerful sorcerer: which was how he was able to achieve so much chaos to begin with.
In the end, Kirby fought Yin-Yarn and destroyed him. However, his knitting needles revived him as Mega Yin-Yarn. However, Meta Knight transformed Kirby into a Tankbot, who shot missiles at Mega Yin-Yarn and destroyed him for good before he and Prince Fluff threw the knitting needles into the distance.
- Yin-Yarn being revived in a more powerful form also happens with Myotismon from Digimon.
Kirby: Right Back at Ya!