Percussive non-tonal Note in Melodic Staff

Question

Would like to make the final note in this passage non-tonal, like and x with a stem, or percussive note:

\times 2/3 { gis gis gis } gis4 cis |

Answer 1

To make a note head x-shaped you can use an override. In your example that would be:

\times 2/3 { gis gis gis } gis4 
\once \override NoteHead.style = #'cross
cis |

Answer 2

This can be done with the \xNote{} command or \xNotesOn and \xNotesOff. See the appropriate section of the documentation: §1.1.4 Note heads:

c4 b
\xNote { e f }
c b < g \xNote c f > b