For Relic Approach, I trained Scorpions only (I think there where 7) and upgraded to Canister Shell. Then, I sent them directly to the refinery (I also sent 1 marine squad to get the Warthogs, which I apgraded to RPG to destroy the shield generator with one hit). After that, I sent the tanks to the Covenant base to attack it from behind, I think it’s easier this way because there aren’t so many Hunters that can reach you there. I used some kind of Hit and Run tactic: go, use Canister Shell to kill/destroy pack of Hunters/turret/main base, and then retreat. I suggest you save before each attack, and if you like the results and didn’t lose any tanks (which is important) then save again (remember to heal, of course). It’s kind of complicate; sometimes you gotta control each Scorpion individually to fire two Canister Shells at one pair of Hunters and still be able to destroy another one with another two shots. Also, you can kill those Hunters with normal shots by concentrating all the Scorpions’ fire at one pack. Sometimes you rely on luck, which is why I suggest you save and load a lot as needed. It’s worth mentioning that activating the Sugar Cookie (which I did, yay!) helps a lot; and at the end, right before the mission ends, activate all the debuff skulls to reduce the point’s penalty (which isn’t so bad if you do it fastly). Also, for the final part, I made a run with all my tanks to the detonator, sometimes using one or two Canister Shells to kill the Hunters in the way. I made it to the end without losing any tank!
In Arcadia Outskirts (again, I used Sugar Cookie), at the start, I took the lower path and left one marine squad at the Reactor (they are safe there, even from the Mega Turret!!!) and then used the Spartans to clear the base area (I used them because if they die, I think it doesn’t count for the Combat Bonus. Also, they resurrect, lol). At the base, I put the Rocket Launcher and the Sniper Spartans covering in the debris (they resist a lot). I built a Field Armory to upgrade the Mac Cannon at least to x2, and an Air Pad to train Vultures. Now, this is the tricky part for when the Mega Turret appears (I didn’t try what DHG Siul S249 suggests, but I personally prefer to leave all the Spartans at the base): I sent Forge to the Mega Turret, going directly to where the Spirit was at the start of the mission (you’ll know where it is; it’s kind of close to some Supply Crates), and got the Mac Cannon ready. Just when the Wraith that is guarding the Turret is visible, I shot twice to destroy it immediatly (generally, the Wraith is next to the Turret, so it will get damaged too). Forge (whom evaded the first Mega Turret shots) can easily clear the rest of the enemies around. Now, leave Forge right south of the Turret, almost hugging the wall, and he can take the Mega Turret by his own! But (which is why I said it’s tricky) sometimes the Turret will aim at Forge (I think it happens randomly); at this moment you have to move Forge to the north of the Turret and then return to the “hug the wall” position; don’t take him too far or he could call the attention of enemies if there are some going towards your base. I really suggest you save now and then while you are managing your base and keeping an eye in Forge. Everytime you dodge a the shots, save; if he dies, load. Eventually, you’ll destroy the Turret and you can build the 2nd base and defend it with turrets and Forge only. When you train 3 Vultures, it’s a piece of cake (I even destroyed the Covenant base just as the Omega Team appeared!).
For Scarab, DHG Siul S249’s suggestion is perfect. That’s kind of what I did, and it worked. Again, I used Sugar Cookie! It helps a lot when facing Hunters.
Repairs is kind of a unique level. It’s really annoying, but I discovered a “secret” thanks to a YouTube video. You don’t have to get the optional Spirits mission! You can get exactly the 32000 points for the gold medal with only the main objectives. I found out that the more units you create, the harder it is to get a x10 in Combat Bonus, so I basically did this: 1st, sent the lonely Cyclop to repairing; 2nd, took the 2 Hawks to the core; 3rd, built the 4 turrets in the Spartans/Wolverines area and leaved those units there; and, from this moment, I alternated between healing the core with the Repair ability, and training Cyclopses BUT just until I got 12! Believe me, I trained around 20 once, and got a really low Combat Bonus (don’t know why). Just try to not get past 12. Also, at some points, I improved the 4 central turrets to anti-infantry and built the 2 turrets in the core area. Of course, I activated Sugar Cookie, and, right at the end, when Cutter says that the core is repaired, I activated the debuff skulls (I discovered also that the skulls’ bonus/penalty applies only to the objectives that get completed after the skulls are activated. So, because all the objectives in this mission get completed at the end, you get all the bonus of the debuff skulls, denying the Sugar Cookie penalty and giving you a little more, 280 points to be precise). If you do all of this, you’ll get 2000 for objectives, 20000 for Combat Bonus, 10000 for Time Bonus and, if using the skulls, 280 or more, totalizing 32000+.
Here is the link to the video:
Mission 12: Repairs - Legendary - Gold Medal
Let us know how it went!