... I feel inspired now, so I'm going to go over what each of the eight-element FVMs would look like.
Darkness & Water - This is what we've got; summons a dark mist. Enemies are worn down by ever-changing phantoms.
Darkness & Fire - Summons clouds of floating ash. Enemies are smothered by chocking heat.
Darkness & Wind - Summons a ranging storm. Enemies find their attacks and movement hampered by buffeting winds.
Darkness & Earth - Summons a dark miasma raising from the ground. Enemies find their footing unsure, with the ground turning to quicksand beneath their feet.
Darkness & Mountain - Summons the shadow of a mountain. Enemies are burdened by a crushing pressure that needs to be overcome with every motion.
Darkness & Lake - Summons a pool of lingering darkness. Enemies find themselves sapped of the will to fight, and of their Qi besides.
Darkness & Heaven - Summons a thundercloud, filled with flashes of brilliant lightning. Enemies are hit with said lightning.
Darkness & Thunder - Summons a thundercloud, filled with booms of echoing thunder. Enemies are rattled to the bone.
Slight differences:
-Fire is all about consuming, devouring, strong while fed, but transient when the fuel runs dry.
--Fire + Darkness would emphasize the Hunger element, dropping the subtle aspect for a field of cursed black fire that is expensive to upkeep, but which feeds upon its victims so you can pay for it.
--Fire + Water would be napalm. The high damage low duration fused with the low damage high duration burns combine to spray lava. I think rather than area based it'd be sticky fire.
-Wind is about freedom, movement and loss of control.
--Wind + Darkness would look very similar, but most likely would be a field of shadows that misleads and misdirects distances rather than savage mist that bites. Just get people walking in circles around you.
--Wind + Water replaces the mists with a storm vortex, throwing attacks off in all directions, where only potent ranged attacks can stay on course, and the storm scours at all within it's compass.
-Earth is about passivity, absorbing energy and generally not doing anything at all.
--Earth + Darkness then would be something like a gravity field. Mother Earth wants you close to her, she will hug you.
--Earth + Water would be quicksand field, trapping opponents where they stand and slowly drawing them into the deeps.
-Mountain Stands. It is immobile, and imposing. It forces you to confront it or back down.
--Mountain + Darkness would be something like a Fite Me M8 field. Possibly raise the user on a pedestal and forcing opponents to focus on them or take penalties.
--Mountain + Water...difficult to conceptualize, one of them has to take precedence here, but you could possibly change Mist summoning to Wall summoning, or throw in some avalanches.
-Lake is the passive/reflective trap. It takes you by the lizard brain.
--Lake + Darkness would be deceptions, where ultimately you see what you most desire in the world and become unable to act against it.
--Lake + Water would be not that different. You'd have phantoms to charm and phantoms to harm, blended so they cause you to doubt even as it wears at your will.
-Heaven is either ethereal and untouchable, or material and transient.
--Heaven + Darkness would be the 'pure' illusion. Light and Shadow combines to make it a fine piece of theater, but it lacks any bite under the illusions, even if you can depict just about anything with it.
--Heaven + Water would focus more on the lightning and storm aspect, where the mist is interrupted by lightning strikes rather than shadow monsters.
