I found that the explanation and terminology for Gauntlet mode was a little poorly explained. So after playing a bunch and reading a bunch I thought I would write my own guide explaining the things I didn't understand.

When you begin Gauntlet mode you will pick 5 officers from the list of currently unlocked story officers. This is going to be your team until you gain sworn allies, the speed at which you unlock them is semi-random, so pick your A-Team wisely (Personally I roll with Lu Bu, Zhou Tai, Zhong Hui, Wei Yan and Nobunaga Oda).

To unlock more characters for Gauntlet Mode you have to encounter them in the battlefields and when you kill them they have a chance to drop their "Sworn Ally" item. This item allows you to talk to the mystic at the gauntlet camp and use the sworn ally item to recruit them.

Sworn ally items will continue to drop even after you've acquired them, these extra ones can be used on the bonds screen to increase your bond with that officer

A stage will have up to 8 "native" famous officers for each battlefield. These officers will continuously spawn on that battlefield, so if you want to farm a sworn ally or x-weapon item for a specific character its best to target a stage that has them listed in a battlefield. in my experience the officers are revealed only when you have beaten them on that battlefield, not just from them spawning on it, although I might be wrong about this.

LEVELS
A Level is a collection of Stages connected by pathways.

In order to unlock the next level you must complete an Octagon Stage, you don't have to complete every Stage before doing this and going onto the next Level.

STAGES
Stages are the icons on a level; The Square or Octagons you see when you unlock a level. The maximum Miasma level is 100.

Stages cost a coloured crystal (Keystone) to unlock (Red, Yellow, Cyan, Purple).
Completing a Red Cyrstal stage earns you a red crystal, yellow crystal stage gets you a yellow crystal etc.

Replaying a stage will earn you excess crystals, these can then be spent to alter the stages (dont know how this affects the stage as I havent done it, I assume it changes battlefields/officers on it/difficulty)

At first you will only start with one red crystal which you use for your first stage unlock. After completing 4 levels of gauntlet mode you can do new game+ on gauntlet mode and it will start you with a yellow crystal, repeat the 4 levels again to get a start with a cyan crystal etc.

In order to complete a Stage you must successfully complete every Battlefield within it

RED STAGES
Red Stages in this guide specifically means when the text is red, not the colour of the crystal. Red Stages will have the following modifications;

• The chests they contain will sometimes turn red. These chests will always contain "vast amount of materials" and spawn an "Otherworld invaders group"
  
• Officers may spawn as one of several variants
  
• The maximum Miasma level is 120
  
• The "Miasma has suddenly thickened" event can happen. This will boost the miasma level by 20 levels temporarily, you can tell when this is in effect as the miasma level will turn red
  
• Dragon Portals gain extra effects

BATTLEFIELDS
Battlefields are inside Stages. This is listed in the Stage info Box as 'Links'.

To complete a Battlefield you must find the exit Dragon Portal and use it. If there is more than one battlefield to complete for the stage then you all automatically move onto the next one and you will start at max health and musou.

CHESTS:
Normal yellow chests when opened can contain the following:

• A crafting item
  
• Gems
  
• "A vast amount of materials" (multiple crafting items/gems)
  
• You get telported to a random spot on the map
  
• Powerful invaders are sapwned (5 generic officers)
  
• Miasma is absorbed from the area
  
• Miasma is released to the area

SILVER CHESTS:
Silver chests have a beam of light surrounding them and you cannot open them till a certain level of miasma is reached, the miasma level required varies and I have yet to observe any rhyme or reason to it. Silver chests will always become green chests

GREEN CHESTS:
Green chests always contain "A vast amount of materials"

RED CHESTS:
Red chests can only appear on RED STAGES. Normal chests will turn red when a certain miasma level is reached, much like the silver chests turning green. When opened the red chest always contains "A vast amount of materials" and spawns a group of Otherworld invaders.

All portals can be used twice.

The first time you use it one of the effects below will happen.

The second time you use it you will gain Formation Gauge and the miasma level will decrease until it tells you the portal is depleted (usually about 3 miasma levels in my experience)

Using the exit portal a second time will end the battlefield in Victory for you.

BLUE PORTALS
Blue dragon portals can have the following effects:

• It reveals it is the exit (Only one per battlefield)
  
• Boost your stats temporarily
  
• Heal your team for random amounts from +50 buns up to a full recovery
  
• Reveal additional chests
  
• Give you unlimited Formation Gauge

On RED STAGES they can also:

• Freeze all enemies in the area
  
• Remove miasma from the area

PURPLE PORTALS
Purple portals will ALWAYS contain "A scroll of Enlightenment" (A Scroll of Enlightenment is an EXP. Fever)

• Miasma slowly increases the longer you are on the battlefield.
  
• Miasma level varies across the battlefield.
  
• Miasma makes all enemies stronger, more health, more stats, more erratic AI.
  
• Higher Miasma levels generally reward better items.
  
• The maximum Miasma level is 100. On RED STAGES it is 120 due to the "suddenly thickened" event.
  
• Killing enemies increases the miasma level for that area.

Otherworld invaders spawn every 5 minutes and is a group of 5 officers. It is only labelled on the map a single officer (eg. Zhou Tai unit) but is actually 5 of them.

In my experience if you kill the leader and then leave them, they seem to run away or despawn and I can't find the rest of them, usually not a good thing since ideally you want to kill all of them to get the X-weapon materials or sworn ally items.

• You can deploy with 3 different formations. You can check the effects and abilities of the formation form the formation menu in game.
  
  
• The maximum formation level is 10.
  
  
• Formations are unlocked by recruiting specific sworn allies and when you reach a certain number of total sworn allies.
  
  
• Formations have 3 aspects to them: Ability Boosts, Special Effects and Officer Abilities
  
  
• Ability Boosts and Special Effects are always active only while that formation is the currently selected one on the battlefield.
  
  
• Officer Abilities and position within the formation cannot be changed, they are baked into the type of character they are. Officer abilities happen when you use the Formation Gauge.
  
  
• The Formation Gauge is the bar below your 5 officers in the bottom left corner.
  
  
• Press R3 to activate the formation gauge (don't know keyboard binding for it)
  
  
• The little line on the bar shows how much of the bar is used up to activate the formation abilities.
  
  
• When you use the formation gauge the ability linked to each officer in your team will be activated.

CHARACTERS
My personal starting team for Gauntlet mode was;

• Lu Bu - Great wide weapon clearance, with a decent ground R1 spamable attack with a Charge 2/EX attack for targeting officers
  
  
• Zhou Tai - Because he is my Bae ever since Dynasty Warriors 4 and I would die for him. He has a great mosou and Charge 2/EX attack.
  
  
• Zhong Hui - Just spam his aerial R1 and win the entire game, big damage and big area effect
  
  
• Wei Yan - a great spamable aerial R1 attack
  
  
• Nobunaga Oda - a decent spamable aerial R1 attack.

Generally characters that can spam one attack with big damage and/or area are great for farming and clearing. Other good choices;

• Cai Wenji - Aerial R1 spam
  
• Ma Dai - Aerial R1 spam
  
• Xu Shu - Ground R1 spam
  
• Zhang Jiao - Mousou
  
• Motochika Chosokabe - Aerial R1 spam
  
• Achilles - Aerial R1 spam

Please leave other good character and moveset explanations in the comments for me :D

FORMATIONS
Solstice formation - Will teleport you straight to the exit portal. Great for just clearing levels rapidly without actually playing them or for exiting after you collected the last chest, this is unlocked at 95 sworn ally unlocks.

I'm currently in the process of levelling formations, so I just stick with one formation and never change it. But obviously its optimal to start with a scouting formation, figure out what map you're on and the locations of what you want and then swapping between attack/defence formations based on situation, generally I think just going for mad high attack and destroying stuff in one shot is the strategy to go for.

CLEARING BATTLEFIELDS AND LEVELING UP
I usually have one character at level 100 to fall back on as my safety escape officer. the other 4 team members I promote and level up while in gauntlet mode, abusing the purple portals and mystic bells item.

As soon as I spawn in I use a scouting formation and immediately use the formation gauge (usually reveals chest or portals or increases line of sight on the minimap. and then I just run to the closest chests/portals activating them without killing anyone.

Generally I avoid killing people until I find a purple portal and I only activate the purple portals when enemies are close enough for me to level fast, usually I can use a level 1 character and get them to like level 30+ form the first purple portal and all the exp will also become growth points for my other officers.

After I have the portals/chests done I tend to focus on officers, the top of the army list will always how the famous officers first before generics, so I tend to just go in order of names that I recognise to get the sworn ally and X-weapon items. I stick around fighting to a level of Miasma i'm comfortable with usually if I begin to get one shot then I exit the stage.

One I have all chests/portals/officers I care about, I dont generally hang around waiting for green or red chests to unlock, I just get out of there