I just tested it, everything works, but it has same glitch as PS2 version (after winpose, next menu doesnt triggers and game stops at one place). In PS2 version, this was the problem of sound plugin, and solution was to use certain sound plugin (thankfully there was a selection of several ones). My guess is that in Dolphinsomething should be done with sound plugin too.
Right now, you can use Training Mode, and also Battle Mode (where you can select opponent and stage), but game will stop after you watch the winpose. Theoretically you can just quicksave at Battle Mode select screen, then play it and then use quickload after each fight.
Right now I search for the save with everything unlocked to try how hidden characters play, but cant find any saves yet.
Btw Double himself isnt like other chars. Each his form has
-2 normal combo strings
-1 ground special move
-1 air special move
-1 Maximum Drive (elemental powerup that stays on him for some time, it seems Cyclone adds movement speed, Luna adds number of hits to special moves, and Heat adds guard damage)
-1 Half Change (circle through Joker-Metal-Trigger halfs, no energy required)
Double’s first form is Cyclone (and free half changes through Joker-Metal-Trigger)
and you can select as secondary form either Heat or Luna (each of those too has free half changes through Joker-Metal-Trigger)
Which means Double can equip 6 forms out of 9 in one battle, 3 of which (Cyclone) act as basic form, and other 3 (Hear or Luna) as secondary forms that need full Rider Gauge and have limited duration.
Ground special moves of each form (well aerial are pretty generic)
CycloneJoker: Whirlwind does tick damage while lifting Double high in air. Basically an extra jump.
CycloneMetal: Spins staff that creates spinning wind sphere centered around Double and damages/sends away nearby opponent
CycloneTrigger: Chargeable shot, the longer you charge the more wind shots it makes, max charge is an unblockable multi-hitting wind stream across arena
HeatJoker: Some super fash dash to opponent, then uppercut
HeatMetal: Staff hit that stuns opponent, next hit lifts his body on staff and slams into the ground, and third hit onto grounded opponent
HeatTrigger: Chargeable fire shot that becomes bigger and deals guard break upon charging
LunaJoker: A “Get Over Here” move with elongated fist. Dizzies opponent after pulling him up close
LunaMetal: Quick dodge backwards, and attacks place where he just was with staff-whip. Catched opponent is then electricuted with multi-hitting electricity
LunaTrigger: Multiple homing shots. The longer you charge, the more shots will come.
Support Attacks:
Cyclone: Changes to CycloneMetal and walks forward with spinning staff attacks with wind sphere around him + Activates Cyclone element Maximum Drive
Heat: Changes to HeatTrigger and shoots fire shot that leaves opponent burning and constantly losing health afterwards + Activates Heat element Maximum Drive
Luna: Changes to LunaJoker and makes very long stretching punch that sends opponent away + Activates Luna element Maximum Drive
Double has only 1 super, its Joker Extreme