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Mission Difficulty Variety WOTC

Most missions scale in difficulty based on ongoing in-game month. With longer campaigns you always end up in a spot where every mission you get is rated Very Difficult and I find that to be boring.

It also makes the game quite unforgiving as there is very little room to level up new soldiers later in the game if you happen to lose a couple of good ones.

The game has 2 separate scaling systems. Force Level is the alien tech level that goes up over time and allows more advanced enemies to spawn. Alert Level is a mission specific number used to select how many and how big pods the mission should have.

Alert level is composed of many separate parts, but in general it is relayed to the player via the Missions difficulty rating. Special and story missions have it set to a static value, but the regular repeatable mission types simply have it increase over time.
e.g.

Commander uses Veteran difficulties and Legend uses Rookie ones, but as the campaign takes longer you get a lot more Very Difficults.

What this mod does is changes the regular missions to have variance in their difficulty, where earlier missions can rarely end up harder and later missions easier. This mod does not change which enemies are able to spawn; only the number, size and locations of enemy pods are affected.
By default:

The chances and affected mission types are configurable in XComGame.ini.

This mod utilizes a specific quirk of the vanilla mission spawning system so it will most likely not work with mods that alter that. Covert Infiltration has a completely custom mission spawning system and this mod will only affect retaliation missions there.

Use Activity Difficulty Variety CI for Covert Infiltration's Assault and Infiltration missions.