The plot of Kirby's Epic Yarn largely revolves around Nintendo's cutesy cream-puff being dragged out of his normal world by an evil sorcerer named Yin-Yarn and trapped in a fabric-based world called Patch Land. Everything in this new land, including the heroic marshmallow Kirby, is made of yarn and fabric. As a result, Kirby has lost his signature inhalation and power absorption abilities. After meeting and saving Fluff, a prince, Kirby and his companion decide to work together to "stitch-up" Patch Land in the wake of the destruction caused by Yin-Yarn.
Kirby's Epic Yarn follows previous Nintendo franchises Paper Mario and Yoshi's Story in its creative design around physical real-life aesthetics. Where Mario was designed around a flat paper theme, and Yoshi lived though a living story-book (in a sense, a variation on a paper theme), Kirby ventures into strange new territory being made of fabric and yarn. Stages and puzzles are heavily designed around the fabric themes and aesthetics, such as enemies being made out of yarn, and puzzle elements involving zippers and buttons.
As mentioned, Kirby has lost his typical powers, and instead of using his formidable lungs as a weapon, he uses a whip (obviously) made of yarn. While Kirby no longer swallows enemies to steal their powers, he hasn't slowed in the least bit where transformation and unique powers are concerned. Kirby floats by transforming into a parachute, flies as a UFO, drives as a car, and features a wide range of other transformations including an anvil, a dolphin, a mole, a dune buggy, a rocket, a robot, musical notes, and more.
Like the Lego games or later Wario Land titles, Kirby really doesn't die. However, taking damage causes Kirby to lose precious items (colored beads for instance) that the player collects throughout the levels to, in effect, earn higher scores, medals, and to unlock more challenges in the game. As well as the item collection, each stage contains three hidden secrets for players to hunt. Each "world" in the game features a boss battle and extra stages should the player meet the right challenges in item collection. There are also new friends to be made who bring about several smaller challenges such as finding a certain number of characters in a stage within a time limit, carrying a character to a new location, and more.
Also, Kirby's Epic Yarn follows the seemingly current trend from Nintendo of the game playing largely as an old-school side-scrolling title a la New Super Mario Bros. Wii, large segments of Metroid: Other M, and the revamped Donkey Kong Country Returns.
Kirby also welcomes his new pal, Fluff, in two-player cooperative gameplay which adds to the puzzle solving and gameplay in many situations. Like many Nintendo-helmed Wii games, Kirby's Epic Yarn takes liberties with the Wii Remote using it for several different styles of play holding the Remote sideways à la classic controllers, pointing at the screen, or angling the controller for other uses.
The 2019 Nintendo 3DS version further expands the gameplay with amiibo compatibility, new abilities, mini-games and the new hard mode ("Devilish Mode"). The Devilish Mode, which can be chosen at the beginning of each level gives Kirby health (which he doesn't have on the standard mode) and makes a demonic little yarn monster follow Kirby around and drop bombs on him, fire arrows at him, or just try to hit him with a quick dash.