This is an idea for a new type of mission. It would fall into the same category as convoy and supply raids for intel requirements and region progression. XCOM would get a lead on an Advent Laboratory assigned to the Avatar project and be sent in to wreck things in some manner. The actual victory conditions and rewards would depend on how well you can infiltrate it prior to mission launch.
Below 120% infiltration: Tier 1. Neutralize an Advent Scientist working at the site.
120% to 170% infiltration: Tier 2. As above plus upload a Stuxnet-type virus into the Advent network.
Above 170% infiltration: Tier 3. As above plus wipe a large amount of files relating to the Avatar project.
Now for the details. At tier 1 (default) a scientist appears and this works the same as any other VIP mission: capture or kill. If killed, the Avatar project gets delayed by one week. If captured your get the delay and there is a chance that they will defect to XCOM equal to 1/2 your infiltration level at mission start.
As an optional objective there will also be a terminal near the scientist that can be auto-hacked for 5 to 15 bonus Intel. At tier 2 hacking the terminal will automatically delay the avatar project by an additional week. At tier 3 hacking the terminal would also reduce the Doom Counter by 1. Obviously getting those tiers won't be easy.
Advent guard placement would be as normal, with one pod always guarding the VIP and terminal room as per normal as well. Map would likely use Advent outpost tile set. Bonus difficulty: If infiltration dips below 80% then there is a chance that the scientist is actually a Faceless and this was all a set-up.
[Idea] Raid an Advent Laboratory
Re: [Idea] Raid an Advent Laboratory
I feel like the gist of that kind of mission is already in the game - if you find a facility lead and research it, you get to sabotage progress on the avatar meter (facilities in LW2 are completely hidden until you use a lead, unlike vanilla)