3D Medusa colouring spreads across digits, not just one digit. Strong links can be conjugate pairs *or* the two candidates inside a bi-value cell.
Before this: Learn Simple Colouring first.
Why it works
Same colour rules as Simple Colouring, but in 3D: same-colour conflicts, opposite colours in one cell, or seeing both colours still mean eliminations.
You are painting a bigger truth/false map until a contradiction or trap appears.
Demonstration
Colour candidates across digits using strong links (conjugates and bi-value cells).
The green cells show a 3D Medusa involving 7. Watch for colour conflicts in 3D.
Same-colour conflict, both colours in one cell, or seeing both colours — those traps give eliminations.
Apply the medusa eliminations (red) (here 7). Colouring found a conflict or trap.
Example 1
Build a multi-digit colouring map.
Medusa colouring on 3 finds a useful conflict.
Eliminate the marked candidates (red) (here 3). Colour rules forbade them.
Example 2
Build a multi-digit colouring map.
Medusa colouring on 9 finds a useful conflict.
Eliminate the marked candidates (red) (here 9). Colour rules forbade them.