Ben & Holly's Little Kingdom
Elf Joke Day / King Thistle's New Clothes
S1 E108:
The Wise Old Elf plays a trick on Nanny Plum, but she gets her revenge by turning the Wise Old Elf into a snail. Snooty King and Queen Marigold are coming to visit. When the King's new clothes get dirty, Nanny accidentally shrinks them all.