Mongols

[Agent Smith]

Well, what I'm worried about is that if they don't get a settlement, all of their generals will die of old age before I even get a chance to fight them, and then they'll just become some worthless rebel stacks. I know they're somewhere in Russia, but my forces are fighting off Venice (backstabbers), Scotland (idiots), and the HRE (in my way), so it'll probably be another fifty turns before I get to head over to Russia, assuming that the Byzantines (Venetian puppets) or England (probably will backstab me, once I take out Scotland) don't attack.

Send out a couple of spies. You'll find them eventually.

[FactionHeir]

To answer the OP's question about Mongols and Timurids:

descr_strat.txt

faction_relationships 	england, at_war_with 	slave
faction_relationships 	france, at_war_with 	slave
faction_relationships 	hre, at_war_with 	slave
faction_relationships 	spain, at_war_with 	slave
faction_relationships 	venice, at_war_with 	slave
faction_relationships 	sicily, at_war_with 	slave
faction_relationships 	milan, at_war_with 	slave
faction_relationships 	scotland, at_war_with 	slave
faction_relationships 	byzantium, at_war_with 	slave
faction_relationships 	russia, at_war_with 	slave
faction_relationships 	moors, at_war_with 	slave
faction_relationships 	turks, at_war_with 	slave
faction_relationships 	egypt, at_war_with 	slave
faction_relationships 	denmark, at_war_with 	slave
faction_relationships 	portugal, at_war_with 	slave
faction_relationships 	poland, at_war_with 	slave
faction_relationships 	hungary, at_war_with 	slave
faction_relationships 	papal_states, at_war_with 	slave
faction_relationships 	aztecs, at_war_with 	slave
faction_relationships 	slave, at_war_with 	england, france, hre, spain, venice, sicily, milan, scotland, byzantium, russia, moors, turks, egypt, denmark, portugal, poland, hungary, papal_states, aztecs

See this section right at the bottom of the file? You want to make it look somewhat like this:

faction_relationships 	england, at_war_with 	slave, mongols, timurids
faction_relationships 	france, at_war_with 	slave, mongols, timurids
faction_relationships 	hre, at_war_with 	slave, mongols, timurids
faction_relationships 	spain, at_war_with 	slave, mongols, timurids
faction_relationships 	venice, at_war_with 	slave, mongols, timurids
faction_relationships 	sicily, at_war_with 	slave, mongols, timurids
faction_relationships 	milan, at_war_with 	slave, mongols, timurids
faction_relationships 	scotland, at_war_with 	slave, mongols, timurids
faction_relationships 	byzantium, at_war_with 	slave, mongols, timurids
faction_relationships 	russia, at_war_with 	slave, mongols, timurids
faction_relationships 	moors, at_war_with 	slave, mongols, timurids
faction_relationships 	turks, at_war_with 	slave, mongols, timurids
faction_relationships 	egypt, at_war_with 	slave, mongols, timurids
faction_relationships 	denmark, at_war_with 	slave, mongols, timurids
faction_relationships 	portugal, at_war_with 	slave, mongols, timurids
faction_relationships 	poland, at_war_with 	slave, mongols, timurids
faction_relationships 	hungary, at_war_with 	slave, mongols, timurids
faction_relationships 	papal_states, at_war_with 	slave, mongols, timurids
faction_relationships 	aztecs, at_war_with 	slave, mongols, timurids
faction_relationships 	slave, at_war_with 	england, france, hre, spain, venice, sicily, milan, scotland, byzantium, russia, moors, turks, egypt, denmark, portugal, poland, hungary, papal_states, aztecs, mongols, timurids

As a disclaimer, I have not actually tried this, so it might not work. Theoretically it should however.
Let me know if it does or not. If it does, you might want to make some edits to the descr_faction_standings file too, so you don't constantly lose global rep because you are at war with those 2 factions. Similarly, you want to edit descr_campaign_ai_db.xml as well for that so some of the triggers don't always return false.
Alternatively, you can add the war declarations into the campaign_script.txt file so they turn hostile when they actually spawn.

Oh, and you need a new campaign for those.

[Patricius]

The Mongols sometimes do nothing for a long while except move about randomly, and without warning will pile into Antioch, and once taken they fan out.