How to get such legend in MATLAB?

As you can see in the attached Figure, only 6 legends are used. (not 8 = number of curves).

How to do so?

Answer 1

[dpb]

Use the 'DisplayName' property for the desired line types to be plotted -- you'll need two lines drawn with just the solid line and four drawn with just the markers for the legend; they can be dummies containing NaN for data but drawn just to create their line handles of the correct styles for legend

Then, when call legend, pass ONLY these line handles.

See the documentation for legend for complete syntax and examples using other than just the default handles.