Tips for the Final Mission
Playing in normal difficulty, without iron man, I used a squad that relied heavily in stuns and executions to kill fast enough the death guard that keeps arriving. Mainly because I had my librarian, a paladin with a psi-cannon that delivered stuns (especially in powered mode), and an interceptor with a hammer that gives +1 AP twice per turn for dealing crits, +1AP for the skill that does the same, and using a shard to increase that chance to almost 100%
The librarian was very useful to keep teleporting the full squad close to the groups that are packed together, so the psi-cannon and the librarian skill that stuns can do it’s magic to get me lots of executions (careful with wasting too much Willpower, and remember to replenish it) The Interceptor also helped with mechanical enemies, and cleaning separate enemies fast enough.
Inside my strategy wasn’t that much intense. I didn’t care that much about causing damage, but mostly stun Mortarion fast enough. And if possible, using Draigo to pull him away from my knights. Keep distance too. The interceptor I used also was able to have a high chance of crits, plus extra crit damage, spending only 1 point of willpower using the powered melee attack (the regular one) Any other crit dealer, like my purgator, was useful to remove some abilities fast from Mortarion and some of the heavy enemies that assist him.
But my powerhouse was in the yard. A similar composition that I used to kill the 4th reaper in just one turn (or two, I don’t remember, but that mech went down very fast, especially using my tier 3 hammer with extra AP per crit)