Which idiom matches the icy-party illustration?

The complete answer is BREAK THE ICE.

What are the numbered letter mappings in Level 15?

The four missing-cell mappings are 20=A, 23=K, 15=H, and 4=C.

Code Busters level guide

easy

Code Busters Level 15 completes the illustrated idiom BREAK THE ICE. The completion card defines it as making people feel more comfortable.

If the player asks you to sign in, open the video on YouTube instead.

Read BRE__ T_E I_E. together with the illustration and identify the answer BREAK THE ICE.
Enter 20=A in the fourth position of BREAK.
Enter 23=K to finish the first word.
Enter 15=H between the seeded T and E to complete THE.
Enter 4=C between the seeded I and E to complete ICE and trigger the success card.

Guessing a different ice-related phrase even though it does not match BRE__ T_E I_E.
Swapping 20=A and 23=K in the final two positions of BREAK.
Stopping after BREAK instead of manually filling the remaining H and C cells.

Board notes 5 details

Layout: An Idioms board shows an icy-party illustration above the pattern BRE__ T_E I_E. Seven seed letters and four numbered blanks are visible.
Goal: Fill the four missing letters and complete BREAK THE ICE. Then reach the card that explains the idiom's meaning.
Opening: Use the visible BRE prefix and enter 20=A, then 23=K, to finish BREAK.
Danger Zone: Follow the written three-word pattern instead of inventing another phrase from the image, and manually enter each remaining blank when selected.
Mechanics: This image-backed Idioms round uses a picture as a semantic clue; the demonstrated solve enters four cells and leaves all three mistake circles unused.

Which idiom matches the icy-party illustration?
The complete answer is BREAK THE ICE.
What are the numbered letter mappings in Level 15?
The four missing-cell mappings are 20=A, 23=K, 15=H, and 4=C.
What does Break the ice mean in the game?
The completion card defines it as making people feel more comfortable.