The 3rd stage of the annual John Van Caneghem Tournament (2008).

Dear friends, please enlighten me just in case (there was a "precedent"). How is victory determined? Do you need to eliminate everyone, or just someone specific?

You need to eliminate everyone + dig up the Grail.
The winner is determined by the number of points. If the number of points is equal, then by the number of days. If the number of days is also equal, then by the number of demons + horned demons in the hero's army.
Dig up the Grail with the map-puzzle fully revealed.