Arcadia City is impossible to beat.

[Icecoldkila15]

Just to let you know, I have beaten the campaign on both Easy and Legendary difficulties. So it's obvious, of course, that I've beaten Arcadia City at least twice.

I am not currently going after the achievement (who's name I forget) where you have to beat all missions in par-time on Heroic difficulty. Should be simple enough, hence I beat the game on Legendary. However, there seems to be a problem. Easily enough, I can survive flawlessly (without losing any units) until the last minute - where everything goes wrong. Cortanna, or whoever the blue-human internet person is, comes online and warns me of some sort of Covenant gun that will soon be online. Of course only having one minute left; I think nothing of this. Now, there's only thirty second left in the game. I believe I have won. Right? Wrong! Two beams coming from an area out of view and out of recognition hit Cargo 2 and destroys it within 1 second. Twenty minutes of my life - gone! I was angry but content enough to restart the level. This time during that last minute I placed over 15 Hornets above Cargo 2 as a pathetic attempt as a shield. This failed as well, costing me the mission.

My question is "Is this level winnable?" and "Why is it happening now and not on Legendary?"

[M1GHTY M4VS]

wouldn't beating the level in legendary under par time solve your issue at all ?

[Tai_MT]

The level is winnable.

My friend and I had issues with this level as well on Legendary Difficulty during Cooperative.

There are two solutions.

The first solution is to keep TWO transports alive as long as possible using NOTHING BUT Warthogs with Gauss Cannons. Place half at one transport, half at the other. You cannot afford to lose EITHER if you wish to survive the Covenant Super Cannon. Also keep in mind you can use your "heal" ability or even "MAC Rounds" if you need to.

The second solution is to pay the Covenant base a visit. No, you are NOT going to beat the base. I've yet to find a way to kill it without losing a massive amount of units and failing the mission. You visit the base for ONE reason. You kill that cannon. Get some units up there and attacking it, then drop some MAC rounds on it. Destroy the cannon at all costs and it should help you out.

Anyway, those are the only two solutions I've ever found for beating that mission. The mission after it has a Super Cannon as well. We beat that by rushing where it spawns and building before it could get up and running.