In Grow a Garden, pets have abilities that can apply mutations, duplicate crops, increase variant chance, and more.
Players start with 3 pet equip slots, but can get up to 8 pet equip slots by trading in aged pets.
You can obtain pets by buying Pet Eggs from the Pet Shop or Event Shops and hatching them.
To hatch an egg, you must place it on an empty spot in your garden and wait for the hatching period.
This article contains an Headless Horseman pet wiki in Grow a Garden, including its trading value, price, ability, chance, and more in Roblox.
Grow a Garden Headless Horseman Pet Wiki

The Headless Horseman in Grow a Garden is an Prismatic pet that was added in the Ghoul Garden Update.
You can obtain it from the Spooky Egg at a 0.5% chance.
To obtain the egg, you must submit requires fruits to the cauldron or the jack-o-lantern, or purchase it from the Creepy Critters shop.
The Headless Horseman resets a level ~50 pet without a mutation and gives it a chaotic mutation.
Further reading
Grow a Garden Fortune Squirrel Pet Wiki