Preheat the oven to 400°F. Oil a large baking sheet or use parchment paper.

Whisk the soy milk and vinegar and set aside. (While it stands, it will curdle and thicken, creating a vegan buttermilk substitute. This only works with soy milk; if you use a nut milk or coconut milk, it will not thicken.)

Mix together all of the dry ingredients in a large mixing bowl. In a smaller mixing bowl mix together all of the wet in a medium sized bowl - including the milk vinegar mixture.

Add the wet to the dry and mix with a wooden spoon until you need to use your hands. It is possible that your mixture may be too wet depending on your purple sweet potato puree. If that's the case, add more flour until it's thick enough to pat out with your hands.

Pat out the dough on a floured cutting board. I used a skull cookie cutter, but you can use a glass or other shape if you prefer.

Cut out the biscuits and carefully transfer them to the prepared cookie sheet. Pull the leftover dough together and pat out again. Repeat until all the dough is used.

Decorate your biscuits to look like monsters.

Bake until the bottoms are lightly brown, about 15 minutes for large biscuits.