Built-in Cosmetics are Cosmetics that can only be used with a certain Cosmetic Item. Although, there are some glitches that contradict this, for example with Go Cat Go, which may have hilarious results.
The first of these were the Built-In Emotes, introduced in Season 6, but only officially referred to as that in Season 9. In Chapter 2: Season 4, other Built-In Cosmetics were created as well.
Built-In Emotes that are useable by Sidekicks are referred to as Sidekick Emotes.
 |
 |
 |
 |
 |
| Back Blings | Pickaxes | Gliders | Emotes | Sidekick Emotes |
|---|
 |
 |
| Wraps | Former |
|---|
Back Blings 
Pickaxes 
Gliders 
Emotes 
Sidekick Emotes 
Wraps 
Former 
The following cosmetics used to be Built-In to certain Cosmetic Items however where changed at some point to be universal.
Trivia
- Built-In Emotes will appear in the Locker's section of your Emote Wheel in-game.
- While most Built-In Cosmetics are assigned to one Outfit only, both Mjolnir and Reformed Mjolnir are assigned to Thor, Captain America, Thor Odinson, Mighty Thor, and Moon Knight.
- With Captain America specifically, this is due to him being worthy of the Mjolnir in Marvel's canon.
- If an Outfit unworthy of wielding Reformed Mjolnir attempts to do the Bring The Hammer Down emote, a unique animation will play where Mjolnir falls onto the ground as the character struggles to pick it up. This can only be seen if the player somehow equips Reformed Mjolnir with an unworthy Outfit.
- This may have suggested that at some point, other outfits were planned to able to use Mjolnir.