Ice/Slippery Surface

Source: Paizo Blog

A frozen lake, a sheen of thick ice on a dungeon or cavern floor, or some other cold and slick surface, slick ice can be hard to traverse, but can also increase the speed of creatures that are agile or foolhardy enough to utilize its surface’s lack of friction.

A creature traversing slick ice at more than half speed is required to make a DC 15 Acrobatic check at the start of the movement. Failure causes the creature to fall prone at the start of the movement. Running or charging on slick ice increases the DC by 5, with the same effect on a failed skill check. A creature that succeeds at this check by 5 or more can increase its move across the ice by 10 feet, but is considered flat-footed until the start of its next turn. Creatures (like those with enough levels of barbarian or rogue) that can’t be caught flat-footed at the start of combat are immune to this flat-footed effect as well.