Sent in to "retrieve" a doctor at a gene therapy clinic who apparently had some information the Spokesman wanted on the Avatar project. We managed to sneak into the clinic, but a patrol followed us to right outside the door - a Muton, Advanced Trooper, and Advanced Lancer. Since the extraction point was literally a bit outside the opposite door, I sent one soldier on ahead to grab the target wile the others simply overwatched up and ripped them to pieces. I was patting myself on the back for about five seconds until a second patrol, this time an Archon with two Mutons, charged in through a window and set up in the right room off the entrance. A reinforcement beacon went off on the extraction point, and opening the door to prep my escape revealed another pod (which I expected)...various mechs and shieldbearer, one of which immediately overwatched (which I didn't). The kicker was that I had five turns to extract, and three of these would be needed just to reach the LZ for my furthest troops. Rather than take the risk of a lucky crit ending the mission, I dinged the overwatch mech with a Haywire stun and immediately had the soldier who captured the target dash out and evacuate.
Mission accomplished but effectively down a soldier now, I ended up in a massive moving firefight as I pushed as recklessly as I could. I took down the Archon with combined fire, both Mutons with two Acid Grenades (plus two turns of burn damage; a Flashbang was perfect to keep them locked down while they took their time dying), and the advanced mech (which lit up my cover with a burst attack that put the exit in flames) with more focus fire, then cleared the enemy out of my path with incendiary grenades. By the end of it, the gene therapy clinic was in flames, half of the enemy soldiers (including the most dangerous) were down, and my team was assembled out in the open at the LZ. Two-thirds of my team came out with grievous wounds, but they all came out at the very last second, and the surviving ADVENT soldiers came out with a fresh appreciation for the insane fanaticism of these XCOM terrorists. The two uninjured were the soldier who grabbed the target and my first novice psionic, who I sent because I thought the mission would be a milk run.