My Tokyo Marui P90, my favourite & one of my oldest guns.
Doesn't look much different to stock externally, but it's had a few upgrades:
G&P metal upper receiver
Prometheus 6.03 barrel, Prometheus purple hop rubber, AirsoftPro "stability snob"
Guarder air seal nozzle, Guarder steel cylinder head, Guarder chromed cylinder
Guarder polycarbonate piston with Systema Area 1000 aluminium piston head
Guarder SP90 spring
Prometheus bearing spring guide
Systema oilless metal bushings
Prometheus hard cut-off lever
Stock motor & gears
Wired with a basic MOSFET (IRF2804, used to have an active braking MOSFET module fitted but replaced it as it made the main spring make a "boing" noise after firing whenever it was fired on semi auto), blade fuse, Deans connector
Does a little over 330fps