This is the stuff i checked.
missing:
- cursor-smoke
- mania-key1
- mania-key1D
- mania-key2
- mania-key2D
- mania-keyS
- mania-keySD
- mania-note2L
- mania-noteSL
- mania-stage-left
- mania-stage-right
- mania-stage-hint
not implemented / not skinnable:
- selection-mod-fadeout (technically "Hidden" in mania)
- ranking-background-overlay
only used by default template / not skinnable:
- scorebar-marker (new default scorebar has different behaviour than normal scorebars, it changes colours when near the critical zone aswell as the marker)
skin.ini:
[General]
CustomComboBurstSounds: 30,60,100,150,200,250,300,350,etc. (every 50)
LayeredHitSounds (first time I hear about that line, what does it change?)
[Colours]
//SliderTrackOverride: 0,0,0 (not default but an additional option)
edit: read that sliderb-spec and sliderb-nd might be skinnable in the future. I only checked on current knowledge of mine. still hope that fadeout will be supported one day.