Mission 34 - Breach: The Quadruped Fortress
After several missions where you've had no choice but to be beaten on by the seemingly invincible Quadruped Fortress, you finally have a chance to take it down. Watch out though, as the fortress will use every single one of its advantages to make sure that you don't. To start, move in on it and try to get under its legs. By the time you do, its main chain gun will have begun firing. Take it out quickly with a heavy weapon to get rid of one of the biggest threats this fortress has. Soon afterwards, the laser cannons will start firing in on you as well. Here is where you have to make a choice. If you have enough armor, you can try your best to stay under the fortress and take out the enemies as they are deployed and ignore the lasers until you have a chance to attack them while the hatch is closed. You will suffer a ton of damage from the accurate fire of the fortress, but this is the quickest means to beat the fortress. The other strategy is to move out of range once the lasers start firing and to then take down all the weapons on the fortress itself. Once this is done, it is a much easier task to move in, take down the enemies that are deployed from the fortress' hatch, and attack it whenever the hatch opens. This method is very time intensive as the fortress is slow to move, but it’s a lot safer.
Above: Beware of this thing's Genocide Cannon - it's aptly named
Mission 53 - Starship
It’s time for you to take on the Mothership. You have a small team of soldiers left, all armed with the newest in technology, the Zero Laser Rifle. These rifles fire off power beams, taking down both Gunships and Walking Arms with no real effort. All they need is a clear firing line and they'll do most of the grunt work for you. To help with this, bring along a nice rocket launcher, like a Stingray, that can quickly take down the buildings in their way. Combine this with a Sniper Rifle for the long ranged shots against the Walking Arms and The Mothership.
To start the mission, take down the two visible carriers to stop the Walking Arms from constantly spawning. These Walking Arms are all armed with plasma cannons, and their long range bombardment is not welcome. Once the carriers are down, turn around and run to the building behind you which has a staircase leading up to the roof. It will take a minute to get up there, but once you are, you'll have an unparalleled view of the area. From here, you can take down the buildings to get your troops to attack the Walking Arms, and shoot at them yourself. Make these your primary targets. At some point, possibly even before the Walking Arms are all destroyed, the mothership will drop out its Genocide Cannon. When this happens, drop everything and DESTROY it. If you don't, it will likely kill you when it fires, or at least kill off all your remaining EDF soldiers.
Once the Genocide Cannon is down, the Mothership's weak point is visible. Much like the UFO carriers and Quadruped Fortress, the glowing red light at the bottom is the key to taking it down. Hit it with everything you’ve got. Once the Cannon is done for, it will drop off the hexagonal plates that are ringing it, which turn into plasma launchers and lasers. There are over 200 of these total, although the bottom half, the plasma launchers, are the more dangerous, as they will knock you off your feet, as well as destroying the building you are on (if the Walking Arms didn't do that for you). Use your sniper rifle and fire at the lower hexagons, taking out any of them that have a direct firing line on you, while attacking the red weak point when it shows. If you move fast enough, you can keep any of the launchers from having a good shot at you, and you can weather the lasers the upper shields fire.
Once the mothership has taken enough damage, it enters its final phase, and pulls out the not-quite-so-big-as-the-Genocide-Cannon guns. These huge cannons fire off balls of green energy which act much like the Walking Arms plasma cannons, and will take your feet out from under you. The cannons can be destroyed, but all of them are able to attack at once, due to their placement, so it is best to just keep moving (your building will be gone in the first fusillade) and fire at the Mothership's weak point every chance you get. If you get a breather, take out some Gunships for some health, and soon, the mothership will come crashing down, granting you victory and saving the Earth. EDF!!!