Wigglytuff is available in Pokemon Sword and Shield's first DLC pack the Isle of Armor.
To find out how to evolve Jigglypuff into Wigglytuff, read below.
Moon Stone
According to Wigglytuff's Bulbapedia page, to evolve Jigglypuff it must be exposed to a Moon Stone.
To get one, head to either the Lake of Outrage or Dusty Bowl.
At the Lake Of Outrage near a Watt Trader are eight stones, check under them and there may be a Moon Stone
In the Dusty Bowl there will be some barren trees between a wheat field and a grassy rock, check under the stone there.
