Supply ship

You usually don't want to shoot these down, as most of them actually land for supply missions to alien bases. You can get a nice steady supply of elerium this way.

Unless I'm sorely mistaken, it has 3 power sources and a bunch of navigations... 3 or 4 I think.

Best tactic here involves a 2 stage attack on the ship: securing the doors and securing the lifts.

Once you have moved soldiers onto each of the one-square lifts on the ground floor, you can prepare for the final assault at some leisure, due to the aliens' typical reluctance to shoot straight down a gravlift. You can, of course, shoot straight up at them.

The assault on the middle floor can be executed as a pincer attack from both lifts if you cut through the wall of the three-story lift with heavy plasma.