Game concept
Extreme Game Rule
From the game's encyclopedia
This Game Rule makes the game significantly more difficult.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Extreme Game Rule is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "This Game Rule makes the game significantly more difficult." Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
for a guide, post or blog
Source: game/common/game_concepts/00_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.