Grease

A mischievous curse from a forgotten alchemist, or a black, sticky liquid drawn from a pool of chaos.
 The ground touched by this becomes covered in an unbelievable slickness, even the firmest earth, mocking all who tread upon it.
 Even the most steadfast footing is powerless before this cunning trap; 
small variable beneath one's feet can overturn everything.

i make fantasy, medieval lora. suggest me in comment!