What is the default Mongol Invasion game rule in CK3?

Default: The Mongols will invade around the year 1200, permanently disabling the Become the Greatest of All Khans Decision. If Temüjin dies without forming the Mongol Empire, the Invasion will be delayed at least 50 years. (patch 1.20.1.2)

Does changing the Mongol Invasion rule disable achievements?

Yes for “Never”: the file gives it the flag blocks_achievements. The other settings keep achievements on.

Game rule · Difficulty · Historicity

Mongol Invasion

Default
Never ✕
Random

Mongol Invasion is a game rule in Crusader Kings III (Difficulty and Historicity) with 3 settings: Default (the default), Never and Random. “Never” disables achievements. Patch 1.20.1.2, from game/common/game_rules/00_game_rules.txt.

This section as JSON: /raw/game-rules.json

Quick answers (2)

What is the default Mongol Invasion game rule in CK3?: Default: The Mongols will invade around the year 1200, permanently disabling the Become the Greatest of All Khans Decision. If Temüjin dies without forming the Mongol Empire, the Invasion will be delayed at least 50 years. (patch 1.20.1.2)
Does changing the Mongol Invasion rule disable achievements?: Yes for “Never”: the file gives it the flag blocks_achievements. The other settings keep achievements on.

3 settings

Default
Default
The Mongols will invade around the year 1200, permanently disabling the Become the Greatest of All Khans Decision. If Temüjin dies without forming the Mongol Empire, the Invasion will be delayed at least 50 years.
default_mongol_invasion
Never
Disables achievements
The Mongols will not invade.
The script checks it 2 times, in 2 places
Decisions 1
- Become the Greatest of All Khans
On actions (the game's own hooks) 1
- yearly_global_pulse
Every has_game_rule = never_mongol_invasion in game/common and game/events, by the top-level object it sits in.
never_mongol_invasion
Random
The Mongols will invade at a random date. Thus, the Become the Greatest of All Khans Decision for Nomadic rulers can be permanently invalidated at any time!
The script checks it once, in 1 place
On actions (the game's own hooks) 1
- yearly_global_pulse
Every has_game_rule = random_mongol_invasion in game/common and game/events, by the top-level object it sits in.
random_mongol_invasion

Source: game/common/game_rules/00_game_rules.txt line 805 (key mongol_invasion), modifiers from game/common/modifiers, names from the English localisation; Crusader Kings III 1.20.1.2.