All collectables within Cobra Kai fall into one of three categories:

1. Challenge group collectables
   
2. Mission S rank collectables
   
3. 'Hidden' collectables physically present within missions

The latter two groups can be completed by either Dojo in either a clean save or in NG+.
(for more details see my general 100% completion guide).

Both hidden collectables and S rank collectables are shown in the mission select screen with the rank collectable always at the end. i.e. if in the mission select screen you ever see the following:
Then there are no more hidden collectables to find and the only task that remains is S ranking the mission.

Once obtained each collectable will also unlock either a gi "trigger" or a headband "effect" that can then appear in missions as pickups after defeating enemies.

Combo score thresholds referenced from:
https://www.trueachievements.com/a310548/cobra-kai-wiki-achievement

1. Zone based scoring
   
2. Mission based scoring

For each 'Zone' in a mission you receive the following score based on the highest combo that you achieved within that zone:

• D: 1500
  
• C: 3000
  
• B: 6000
  
• A: 8000
  
• NM: 9000

In addition if you are able to complete a zone without being hit the crown besides the zone will be filled in the zone list and you will receive a bonus 1000 points.

Over the course of a mission 6 'Cool Feats' are tracked:

• Environmentals: 500 points for each enemy finished with an environmental attack (max 2500)
  
• Ultimate eliminations: 500 points for each enemy finished with an environmental attack (max 2500)
  
• Ground Eliminations: 600 points for each enemy finished with a ground elimination (max 3000)
  
• Characters alive: 1000 points for each living character at the end of the stage (max 4000)
  
• Full Health: 1000 points for each character with full health at the end of the stage (max 4000)
  
• No Food: 3000 points if no food was consumed at any point during the stage

Since each mission has at least 2 zones, by far the biggest single contributing factor to rank is combo. The difference between A rank and NM is small but if you aren't completing most zones within a mission with at least a combo of A rank then it is almost impossible to S rank a mission.
Achieving high combos requires two things:

1. Using varied attacks and combos since repeated attacks contribute less to increasing your combo
   
2. Not being hit

For criteria 1, as long as you're mixing and matching the following you should be able to consistently hit a NM combo between 50 and 100 hits:

• Punches
  
• Kicks
  
• Ground attacks
  
• Dojo Skills
  
• Personal Skills
  
• Ultimates
  
• Parries

Some of these are more important than others, however. Landing a single ultimate on a group of 3+ enemies is usually enough to bump your combo up a full letter grade, for instance, and is extremely useful for reliably taking you up from B/A to A/NM.
Different combinations and timings of punches and kicks also result in unique attacks which more quickly fill up the combo meter. If you're constantly button mashing try slowing down and being deliberate with your timings.

For criteria 2, the most important thing is to lean heavily into the invincibility frames. You are immune to combo breaks while performing any of the following actions:

• Performing any Dojo or personal skill excluding Daniel's 'focus heal'
  
• Dodge rolling
  
• Performing an ultimate
  
• Performing a parry
  
• Having the parry stance active (even if damage is taken)
  
• Performing a throw on a grabbed enemy
  
• Performing the animation for an environmental attack

Achieving high combos is about learning how to chain these actions together alongside moves that stun enemies such that you have no window to take damage. You can also cancel any action into a Dojo or Personal skill in order to extend the length of invulnerability which is extremely useful when fighting enemies like the segway mall cops who are immune to stun and inflict passive damage.
For that reason I also strongly recommend that you focus on reducing cooldowns when picking upgrades over increasing strength.

• You can carry a combo between zones if you move fast enough and attack enemies with large AoE attacks while far away/offscreen.
  
• Skipping optional challenge zones completely removes them from your score card. That means you're leaving 10000 points on the table if you don't complete the challenge rooms in the Shopping Mall, All Valley Tournament Arena, West Valley High School and Valley Fest
  
• Each zone only tracks your highest achieved combo. Once you hit NM a single time within a zone, you can drop your combo and focus on map collectables or mission objectives if you want.
  
• Using a single character not only allows you to max them out faster, but it also guarantees 7000 points at the end of the mission if you keep them alive. There is almost never reason to switch characters within a mission.
  
• The 3000 points from no food usually isn't critical to achieving an S rank. Particularly on longer missions if you're struggling to keep your characters alive then you can just sacrifice the score.
  
• "Characters living" and "Characters at full health" are both capped based on the number of characters in your party. If you are struggling with S ranks on early missions then attempt them again after recruiting all 4 Dojo members
  
• Jump kicks will always knock enemies to the ground if you want easy ground/parry finishes.

Each of the 8 challenge groups within the dojo rewards a corresponding collectable upon completion listed below. For specific advice on how best to complete each challenge group, see my 100% guide.

Warming Up.

Skill Master.

Combo Freak.

Environmentalist.

Specialist.

Surgical.

Rivalry Dominance.

Karate Champion.

The rest of the guide consists of collectables gated behind mission completion grouped by mission and titled by gallery number (#??).

In some cases the exact correspondence isn't known (because there's more than one hidden collectable of the same type in that mission) and in those cases "(order unknown)" will be added at the start of that mission's section. If you're able to disambiguate any of those sections I'll update the guide.

Impossible to miss after defeating Derek.

S Rank

Impossible to miss after car park area.

Hidden inside a box before the final boss

Hidden inside a box within the courtyard

S Rank

Impossible to miss in alleyway

Turn left instead of right after exiting the alleyway before the final boss.

Hidden in a box by the electronic sign in the first area.

S Rank

Hidden behind the counter next to the fight with Brucks

Behind the table in the health room immediately before the Kyler fight

S Rank

(Order unknown)
Impossible to miss after turning into the garden

Inside a box on the outside of the fence as you're exiting the gardens

Turn left instead of right after the gardens section to find a small challenge arena. The collectable is in the small garden after completing the challenge.

S Rank

(order unknown)
Hidden in a box immediately after entering the park

Impossible to miss before entering the final zone.

Continue right instead of entering the boss arena.

S Rank

(order unknown)
Hidden at the bottom of the screen in the offices after the showroom.

Impossible to miss in the rear left corner of the parking lot after fighting Lindsay.

S Rank

In the background behind the advert screens in the first mall area.

After fighting Shawn, turn left instead of right after exiting the room to find a secret bonus challenge room.
Beat the challenge to unlock the collectable.

In the food court before the escalator inside a sign in the back.

S Rank

Impossible to miss in the dining area

Hidden in the back left corner of the petrol station

S Rank

Hidden in a box on the right of the outdoor area.

Impossible to miss within the parking garage between the cars

S Rank

(unknown order)
Hidden behind a pillar in the highstreet area.

Impossible to miss before the road

Inside a box on the left after descending the stairs.

S Rank

Hidden behind the red car in the outdoor area.

Hidden in a box in Raymond's boss room.

S Rank

Impossible to miss in the background of the first area.

Impossible to miss in the middle of the road in the first boss room.

S Rank

(order unknown)
Hidden behind the table in Derek's boss arena

Hidden in front of some floaties in the final poolside area.

S Rank

Impossible to miss on the decking

Hidden inside the sign in the carlos miniboss arena.

S Rank

(order unknown)
Behind the reception desk in the first area.

Impossible to miss in the Bert/Nathaniel boss arena.

S Rank

Impossible to miss in the bleachers area.

Head up the stairs in the background after the changing rooms to find a challenge room.
Beat the challenge room to unlock the collectable.

Hidden in the top right corner in the healing area before the tournament mat.

S Rank

(order unknown)
Hidden behind the vendor stand in the first area.

Hidden in a box after the lion statues.

Impossible to miss in the centre of the pavilion

S Rank

Go left instead of right at the start of the mission.

Impossible to miss on a corner.

S Rank

After defeating the first group of enemies inside the bar, head down instead of up.

Hidden in the rear right corner behind the boxes after defeating Graham.

S Rank

Hidden at the front of the screen in the first combat arena of the mission.

Hidden inside a box under the large cobra kai tag before the final boss.

S Rank

Hidden in a group of 3 boxes in the first area.

Impossible to miss in front of some vending machines in the final area.

S Rank

Inside a box in front of the ferris wheel in Kyler's boss arena.

Impossible to miss in front of the sound stage in the final area.

S Rank

Impossible to miss by the lockers.

Enter the door by the previous collectable to find a challenge room.
Beat the challenge room to earn this collectable.

Inside a box near the front of the screen in the wide open area after the lockers.

S Rank

Impossible to miss after the first combat arena.

Hidden in a box one encounter before the boss.

S Rank

(order unknown)
Hidden in a box beside the sports store behind the water fountain.

Impossible to miss by the porta-potties.

Hidden behind a food cart to the right of Jon's boss arena

S Rank

After the Cobra Kai/Miyagi-Do paths merge around the area of the cruz fight there is a challenge room at the bottom of the screen.
Beat the challenge room to unlock this collectable.

In the background between the yellow roller coaster stairs.

Impossible to miss on the stage in the Kyler/Yasmine boss arena.

S Rank