Can someone explain me the use of the fog core?

[Chocos Ramabotti]

On my first playthorugh I'd found a hidden door in the questions level but couldn't get through it. Because I heard so many things about the fog core I thought maybe I'm able to pass it, when using it (on a second playthrough). unfortunlately the door is still locked.
So I couldn't hold myself back anymore and read a guide, but in all honesty, I couldn't really understand the guide. The guide states following:

"1. After creating your backup, go into a branch this is going to be locked, for example, the Ash Branch.
2. Stand in front of the door of the level you are trying to unlock I would use the fog core"

Going into a branch after taking the fog core, but how? The branches are locked I can't go to them.
Standing in front of the door and using the fog core? But how, I did this in the questions level but nothing happened.

So yeah I'm pretty confused and I'm afraid that it's important to do the things in right order or else you habe to start a new games. (back ups on X-Box ONE may be possible, but I'm far to lazy to navigate through all these horrible options.)
Is it possible to play all the levels in one go? The guide rather irritates me.

[DoubleOSpanky]

Yeah, that guide is worded weirdly. I might just make a new guide for that. Essentially, you're on the right track, but a little ahead of where you should be. When you equip the fog core, you block out two wings, 'Ash' and 'Hawthorn'. In a nutshell, you need to get behind the rubble blocking those wings. Secret levels appear behind the piles of rubble.

Here's basically what you want to do. Go into the 'Ash' wing (for the love of Demi, do NOT go into the 'Hawthorn' wing - you'll thank me later), equip the fog core, and enter a level like 'Redeployment'. Immediately turn around and exit the level. You'll now find the fog core is active and you're behind the rubble. You'll now see a new door with scrambled text (level title should be "The Storm"). Once you complete that level, you'll then be able to access the hidden door in 'Questions'.

The reason you want to back up your save is that if you've used the fog core, the changes are permanent. So if you screw it up the first time, you pretty much have to start a new game to try again. Be warned, these levels are by far the most difficult in the game (other than perhaps 'The Storm' arguably -- which is mainly why you want to go to the Ash wing). The levels you'll encounter are easily more difficult than Chains. You're probably going to want to have more than a few power-ups saved up.

[Chocos Ramabotti]

Ok are the level closed after you equip the core, or just when you take it from "another way"? So do I understand right and it's more a decision which wing you want to try? So you can't do the hawthorn secret level and the Ash secret level together, just one of them and then questions afterwards?

That they are more difficult is just fine to me, because chains was still to easy, I expected more from an last level.^^" After the other skull levels that one was not really difficult just the possibilities to do checkpoints were far less.

[Gafgar]

You can do both, as you can access them later, if you beat one of them. If you fail though, both will be locked away permanently after that.

[DoubleOSpanky]

Once you equip the fog core, the next time the hub area loads in, the rubble will block the wings. Taking the fog core from 'Another Way' will simply put it in your inventory. The permachange takes place when you equip it. Unequiping it will not remove the rubble from that point. You would have to return the fog core back to 'Another Way' if you wanted to undo your choice.

Once you do one of the secret levels, the door found in 'Questions' will lead you to a seperate hub where you can do the other secret levels. You will not be locked out of doing the other secret levels depending on the wing you choose.

The level 'The Night' is designed in a way where you are meant to use powerups. You can technically do it without them, but you're probably gonna have a bad time. At least use checkpoint packs your first time.

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Just a question, and sorry for the necrobump: So from my understanding, this secret allows you to unlock two secret maps in the game. To do so, after backing up the save, you go into one of the wings first (so, the Ash wing), then activate the Fog Core, then enter and exit any map, and then beat the new map called "The Storm" and then go into the Questions map and find the secret door for more maps?

Is there a different map if you go into the Hawthorn wing instead? Is it locked off if you go to the Ash wing, or can you access it in the Questions area? Also, what's the easiest way to farm items?

[DoubleOSpanky]

You are essentially correct. There is a hidden level in the Hawthorn wing instead; however, it is easily the most difficult stage in the game ("The Night"). This is why you'll want to go to the Ash wing. The secret area beyond the Questions door is a separate hub world where you can enter all three new levels. You will not miss out on the other levels depending on which one you do first.

The easiest way to farm items is to complete challenges, especially super challenges (when the wisp is golden.) If you don't like the challenge you're on, you can try getting a new challenge by entering/exiting a level or just completing another random stage. Challenges tend to go level by level in a random but directed order. So if you've done a challenge in nearly every stage but one, you're probably going to keep getting that one challenge until you beat it. Once you've completed one for each stage challenges become completely randomized.