Grease

D&D 2014 spell: Grease. Source: Player's Handbook (2014). level 1, school Conjuration, casting time 1 action, range 60 feet, 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.

Source: Player's Handbook (2014), p. 246 - Licenses and attribution