Grease

Source: Player's Handbook
  1st-level conjuration
  Casting Time: 1 action Range: 60 feet Components: V, S, M (a bit of pork rind or butter) Duration: 1 minute
  Slick grease covers the ground in a 10-foot square centered on a point within range and turns it into difficult terrain for the duration.
  When the grease appears, each creature standing in its area must succeed on a Dexterity saving throw or fall prone. A creature that enters the area or ends its turn there must also succeed on a Dexterity saving throw or fall prone.
  Spell Lists. Artificer, Sorcerer, Wizard