The Reaping

The Reaping is the sixth stage of Kane's Challenge, which pits the commander against Reaper-17 in a Blue Zone island city and research facility.

Walkthrough
The player starts with an MCV on an elevated plateau on the south side of of the map. Reaper-17 are located on a similar plateau on the north side of the map, in a well-defended base with numerous Storm columns, Photon Cannons, and Shard launchers. They also have an outpost to the south of there base, near a Tiberium field. Because of these defenses, rushing is not recommended. Instead, the best option is to turtle on the plateau.

Step 1: Guard the Chokepoints
There are three gaps in the cliffs that allow approach to your base. The AI does not seem to use the one furthest from your construction yard, so that leaves two chokepoints to be defended.

First off, construct a Power plant and two refineries, one at each of the two Tiberium fields near your base. Then, build a War factory and a couple tanks and AA-capable units to defend against early attacks. At the same time, get a Command post (or equivalent) completed and build a Surveyor if you are playing as a GDI sub-faction, build a Rig as well. At the same time, you may want to build some air and anti-infantry defenses. Send the Surveyor (and Rig) to the area near the two Tiberium spikes. Unpack the surveyor and, if you have a Rig, place the Battle Base so that both turrets are facing towards the eastern approach. When the Surveyor is completely unpacked, build a Barracks near the Surveyor and train two Engineers to capture the two spikes.

Now you should have a large flow or resources coming in. Build a tech center (or equivalent) and start putting up base defenses and training vehicles (if your playing as GDI or ZOCOM, Shatterers are very effective anti-Scrin weapons) at both choke points. Around this point, the Reapers will definitely be attacking with Seekers, Shard Walkers, Ravagers, and Shock troopers. These attacks will start relatively small, but will increase in size, with Devourer Tanks and Reaper Tripods joining the ranks eventually. If given long enough, they will even deploy an Eradicator Hexapod. Fortunately, the Reapers have no air forces apart from Stormriders, and your Tiberium spikes will provide an endless flow of resources. By the time the attacks start getting heavy, you should have a heavy defense as seen below:

At the chokepoint nearest to your construction yard, you should have:
 * At least 5-6 tanks
 * At least two advanced base defenses (Sonic emitter, Obelisk, Storm column) flanking the entrance to the chokepoint
 * A Battle Base (if GDI) or anti armor base defenses (Nod or Scrin)
 * At least one anti-personnel defense.
 * Some air defenses around the base, particularly near refineries and the construction yard.

By the Tiberium Spikes, you should have:
 * A Battle base (or anti-vehicle defenses) facing both east and west.
 * Two advanced base defenses facing east
 * At least one anti-personnel defense.
 * At least one air defense (unless playing as Scrin- storm column will play that role as well).

Step 2: Prepare to Attack
In between building defenses, build two airfields (or equivalent) and a superweapon. Once you have the Tiberium spike active, you should have plenty of money for both these and the base defenses. Ideally, you should have your superweapon ready before the Reapers do. It is even possible to get it fully charged before Reaper-17 even build a Rift Generator. While the superweapon is charging, start training high-end ground and air units. You can also build a Space command uplink/Tiberium chemical plant/Signal Transmitter for further support powers, or a Reclamator hub (or equivalent) for an Epic Unit if you want.

Once your superweapon is ready, target the Reaper-17 drone platform. This will have the added bonus of destroying the all storm columns, a great deal of the other defenses, as well as enough power plants to power down the surviving base defenses. At this point, finish off the damaged drone platform. GDI and Nod can use Firehawk or Vertigo strikes respectively. For the Scrin, the platform can be taken out by the main strike force, or finished off with the Overlord's Wrath or a strike team sent by Wormhole. You may wish to launch further air strikes or support powers to destroy other high priority targets- the Rift Generator (if the Reapers have one) and a Warp Chasm, again, if they have built one, the Gravity Stabilizer, and surviving power plants. Leave the major power drainers such as the Technology Assembler intact, in order to keep their base defense powered down.

Once you have taken out the Drone platform and shut down the power. You can send the army you built up as your superweapon charged. A group of high-end vehicles, ideally led by an Epic unit should be able to clear out any surviving Reaper-17 forces and destroy the remaining structures. You might want to take out base defenses and power plants first to make sure they remain powered down, then destroy everything else. If you encounter large numbers of buildings garrisoned with Buzzers, you do not need to destroy them, and if you're using a vehicle-based army, they will be of minimal threat. Destroy all the structures at the main and outpost base, and you will complete the mission.

Trivia

 * This stage uses the Safety Nest skirmish map.