Belekor and Dark Rifts

[Green Raven]

How do these work? Do you need to find and secure rifts, or do they just pop out at random?

[Forblaze]

In immortal Empires, He can create them in any province that he has a lord in. As far as I know, they can't be destroyed and only work for him.

[Darth Alpharius]

he has default ones based on his lore like Mordhiem and Southern Chaos Wastes

[Nylan]

Something like every five turns you can create a new rift for your faction. Pretty sure it let me target them on armies or settlements. In the lower right UI above the end turn button is where you find the rift placing mechanic, as well as three other options for whatever. Not at all explained by the game. Bet they expand on that somewhere down the road, but as is the campaigns are just click and figure stuff out. Not the best way to introduce a new mechanic.

[Cryten]

Every 15 turns (10 turns after a tech), and you just need to be able to see an army on the map to summon a portal using your chaos manifestations. So you can send heroes to scout continents and then when you spot an army near where you want to sac, use the ability on them and a new instant shadow portal.

Occasionally the portal ability will reset when Tzeentch enter dominance.