Core gameplay
Some cells on the grid are locked and cannot hold blocks. Blocks must avoid locked cells while forming complete rows. Locked cells disappear after three rows are cleared above them.

Level and content structure
Fifty fixed boards. Each board has a different locked cell pattern. No random generation.

Visual and user experience
Locked cells show a small padlock icon. The icon fades each time a row above is cleared. Background uses a plain grey fill.

Features
A counter shows how many row clears remain for each locked cell. No score display or timer.

User value
Adds obstacle avoidance to standard row clearing. Helps practise selective attention.

Usage scenario
Short waiting periods such as before meetings.