Sirfetch'd is an avian Pokémon that resembles a white duck, standing no taller than its pre-evolved form Farfetch'd and retaining its yellow beak, legs, webbed feet, brown eyes, black eyebrow-like marking, and its stubby tail. It has a crest on its head, consisting of three feathers standing upright. Its wings serve as humanoid hands, with the feathers at the end resembling fingers. It carries a massive leek in two parts, wielding the long, sharpened stalk as a lance and using the hard leaves as a shield.
It is said that Sirfetch'd's evolution was attained by Farfetch'd who have experienced and survived many battles. Sirfetch'd is known to be calm and collected, preferring to fight fairly. Due to its noble nature, Sirfetch'd is often chosen as a motif for paintings; one famous painting in the Galar region shows a Sirfetch'd dueling with an Escavalier. The leek it carries is its most prized possession; it is used as both weapon and food, and maintained for many years. Once the leek finally withers, Sirfetch'd will retire from battle for good.
Sirfetch'd and its pre-evolved form are the only known Pokémon capable of using the Leek item.
Galarian Farfetch'd transferred from Pokémon GO to Pokémon HOME from November 11 to November 16, 2020 erroneously use the level-up learnset of their Kantonian counterpart from Pokémon: Let's Go, Pikachu! and Let's Go, Eevee!. Galarian Farfetch'd or Sirfetch'd in Pokémon HOME, Sword, or Shield with illegal moves had their moves replaced with moves from their level-up movepool on November 16, 2020; opening Pokémon HOME at any point after that date will cause HOME to search all Sword and Shield savefiles on the console and correct the illegal movesets.
Players who transferred a Galarian Farfetch'd with any of these illegal moves cannot trade or battle online with it unless that move is deleted. These erroneous Galarian Farfetch'd otherwise function like other Galarian Farfetch'd, with Galarian Farfetch'd from GO being able to evolve into a Sirfetch'd with an illegal moveset.
Due to a bug in Pokémon HOME, an unnicknamed Sirfetch'd or Farfetch'd from the English, Spanish or Italian versions of the games that is transferred into HOME will be treated as a nicknamed Pokémon, due to HOME assigning a different character for the apostrophe in the species names (i.e. "Farfetch’d" and "Sirfetch’d").
The idea for Sirfetch'd and the giant leek it carries originated from the fact that leeks native to the United Kingdom (which serves as the inspiration for the Galar region) are considerably larger than those native to Japan. In particular, the leek halves are modeled after medieval weapons: a shield and a sword (or a lance). As such, Sirfetch'd may be based on a knight, as well as a Pekin duck.
Like Farfetch'd, Sirfetch'd may be inspired by the Japanese saying 「鴨が葱を背負って来る」, literally translating to "a duck comes bearing spring onions". As a saying, it means "easy target" or "golden opportunity". Sirfetch'd carrying a leek may also be inspired by the fact that the leek is one of the national symbols of Wales, part of the United Kingdom.
Sirfetch'd's appearance may also be based on Sir Lancelot du Lac (literally "Sir Lancelot of the Lake"), one of the members of the Knights of the Round Table. In Arthurian legend, before he revealed his identity to King Arthur, he was known as the "White Knight" for his white armor. The Lancelot leek, which is a wild onion variant named after him, may also be referenced. Sirfetch'd's overall personality may be based on the code of chivalry.
The official Pokémon Sword and Shield website mentions a painting depicting Sirfetch'd battling an Escavalier. This may be a reference to the motif of knights fighting snails, which is sometimes found in medieval and Renaissance manuscripts, as well as Escavalier's own references to medieval jousting.