I skipped that. No need to do something unnecessary.
But here's tips for the Horizon fight and Collector Trap.
1. HORIZON(DUAL SCION+HUSKS)-
You want to run around, in a big circle. Take out the husks first, as they are a huge distraction and get in the way. Be sure to grab the Heavy Weapon ammo and medigel nearby ad your squaddies WILL DIE.
Bring Miranda. She'll die for sure, but Warp is too valuable to pass up.
Once the husks are down(use the SMG to whittle them down, and biotics to kill them quick), focus on ONE Scion.
Running and using the pistol works very well, as it shreds armor.
Also, if you have the chance, use a Heavy Weapon. The Cain saves you a fight. If not, The Collector Beam works, but you have to time your sprint to get out of the shockwave radius.
Once you take down the first Scion, its simple from there.
After eliminating the second Scion, be CAREFUL.
Collectors will spawn to the left of the entrance. Looking from the entrance to the level, go northeast and there will be a little area with cover in the back.
You'll be far enough that you can hurt them, but they won't hurt you. You can also risk going in.
2. COLLECTOR TRAP(DUAL SCIONS+COLLECTORS)
Bring Thane and Miranda for a dual Warp combo. It ANNIHILATES.
Don't waste your time with the Cain, as enemies come in after waves are defeated. Instead, bring the Blackstorm if you have it.
Time your first shot. Ignore the Scion, but as the first 3 Collectors land, hit them with a blackhole.
If you're lucky, all 3 will be bumped off and will die falling before any of them could be controlled by Harbinger.
At that point, another wave will come down. SPAM THE BLACKSTORM.
You should knock down a few, but chances are Harbinger will arise. Take him out as you normally would, but fast-
He goes straight for you and there isn't much cover.
Once that wave is complete, I believe there is one more wave that appears.
While waiting, focus on the first Scion, and kill it with the Pistol/Handcannon and dual warps.
Once the Collectors land, run for cover on the planks that the first group of 3 landed on.
Take out the Collectors, and the last Scion should be easy pickings as it cannot hit you with its Shockwave.
Once complete, you've passed the hardest parts of the game.