For the race, see Demons.
Demon slayer is an achievement/trophy unlocked in Agony and its UNRATED edition.
Achieve requirement[]
This is an alternate achievement to unlock when pushing the Onoskelis off to the Pit in Chapter 1, but leading her to sudden death (hence the achievement's name). To do so, run faster to behind her and quickly push her off.
This can be only achieved in Story Mode.