Tuplet bracket and change staff
This snippet shows how to set a tuplet starting in a lower staff and finishing in the upper one.
aigues = \relative c' { \time 6/8 s4. \stemDown c16[ bes' e] \stemUp g c e \stemDown g8 } basses = \relative c { \time 3/4 \clef F \tweak positions #'(4.5 . 9.5) \tweak edge-height #'(1 . -1) \tuplet 7/6 { c16[ bes' e] \change Staff = md \stemUp g[ c e g] } s4.s8 } \new PianoStaff \with { \omit TimeSignature } << \new Staff = md \aigues \new Staff = mg \basses >>