NOTE: If you're having further issues with difficulty due to mods and what not, how the mod sets up the mission type(s) can be found at XComMissions.ini, located at (wherever XCOM 2 is installed)\steamapps\workshop\content\268500\647242867\Config 

Haven Siege - The local resistance fighters has managed to hold off ADVENT in time for XCOM to arrive, but have been whittled down to their last line of defence. Hold off ADVENT's siege long enough for the non-combatants to evacuate. Any surviving fighters will join up with XCOM afterwards. 

Afterwards, you can try to secure the area after denying ADVENT their goal, or you can just evac the area right afterwards. 


Effectively an attempt at bringing over EU's style of Base Defence as a mission type. The reinforcements will come whether you're done with the current group or not, and you got a whole bunch of enemies you're going need to deal with at the start. (Starting missions should be around the low 40s.) 

PR Tour - Someone high up connected to ADVENT is doing a PR tour in the outlying areas to convince people to move to the ADVENT City Centers. Take care of them while they're out, but be careful, ADVENT's willing to pull out some big guns if the VIP ends up biting it during the mission. 

And by big guns I mean Firebrand stays out of the fight for 2 more turns in addition to the default 8 more turns and the pace of reinforcements increases.

Evac is required for the mission. 

Basically a hybrid of attack and defence, you're given nearly all the time in the world to try setting up, but once you start the fireworks, you better dig in for a bit of a fight. 

Rescue VIP from Rioting City - A relatively ranking resistance member has been captured, but Resistance provocateurs have managed to set off riots to distract ADVENT while XCOM goes in to rescue them. No hard timer, but Firebrand won't be able to stick around once ADVENT gets alerted to the VIP's escape and will need to come around again after 8 turns, and reinforcements will come in regularly. Surviving resistance provocateurs will try to hook up with XCOM and will be willing to help out. 

Adaptation of PR Tour for Council Missions after hearing about Beagle wanting a council mission where you could actually stick a bit and fight in a city center building instead of having to constantly move across the map. Evac mechanics work exactly like PR Tour, you should be able to call it down once the timer has expired. 


Mission types should be grabbed by the game's mission handler without any issue, though it'll be a bit random whether it picks any added types or a vanilla type. 

Resistance fighters that currently spawn in Haven Siege missions can have their equipment upgraded through the Proving Grounds, and if the player enables plasma weapon research in the XComHavenSiegeSettings.ini located at (Documents\My Games\XCOM2\XComGame\Config), the Research Lab as well.
It can also be altered so resistance fighters auto-acquire the latest equipment from XCOM, just set NoTechsRequired to true with either mod configure menu, or altering XComHavenSiegeSettings.ini. (This will also let the mod use mod-added weapon tiers like Lasers or ETC Weaponry)


ISSUES:
Enemies Don't Seem To Be Spawning
Clear out your config files in your Documents\My Games\XCOM2\XComGame\Config folder. Game doesn't like alterations to XComMissions.ini when it's not regenerated.

PR Tour may or may not be related to VIP not spawning on mission? (have yet to replicate this personally) 

Attack of the Resistance Clones! - if the character pool is allowed to be used and a small enough pool is in effect, it may spawn already dead or active soldiers as resistance fighters in Haven Siege and Rioting City Extractions. 

This can be disabled in the XComHavenSiege.ini with OverridePool set to true. 

My resistance rookies can't move! - this seems to be a incompatibility issue with Dynamic Stats Development, as long as it's active it'll cause haven rookies to not function normally. 

I'm using Guerilla War but some of these missions don't follow its rules - go to this mod's XComMissions.ini  and for every IsTacticalObjective=true, set it to false. I set it to true so I didn't have to mess around with how the game defined mission success to work with the base game (in case another mod modified it like say, Guerilla War or mods that make Sweep objectives optional), but it does result in you getting all the loot after mission completion.
Setting it to false will make any missions not auto-collect any corpses after mission completion.

I don't want these rookies, add in a way to get rid of them - There's a dismiss button.

Configurable Mission Timers makes this harder!
Add the following rules to XComTacticalMissionTimers.ini in that mod:
+timerOverrideRules=(objectiveNames[0]="RM_Obj_TerrorDefence", behavior=eTimerRuleBehavior_ADD, value=0)
+timerOverrideRules=(objectiveNames[0]="RM_Obj_RescueVIP", behavior=eTimerRuleBehavior_ADD, value=0)
+timerOverrideRules=(objectiveNames[0]="RM_Obj_NeutralizeVIP", behavior=eTimerRuleBehavior_ADD, value=0)
Second, you can adjust when the mission goes into two reinforcement per every other turn mode (or even just disable it entirely) in the XComHavenSiege.ini in the mod's config folder, located at (wherever XCOM 2 is installed)\steamapps\workshop\content\268500\647242867\Config

Thanks
Mike The Muton for making the thumbnail image.
MantLemon for making the Chinese localization.