PC-88, MSX, PC-98, X1, FM77AV versions developed by Wolf Team (1986–87) note The MSX version, while released at the same time as the PC-88 version, was heavily stripped down to fit on a cartridge
Famicom version (1987) — Though published by Tokuma Shoten, this was Telenet Japan's first failed attempt at console game development; the promotional video made by Sunrise for this version was the closest thing ever produced to a Valis anime.
Mega Drive version developed by Riot (1990), released in the U.S. by Renovation Products
PC Engine Super CD-ROM version developed by Riot (1992)
PC Engine CD-ROM version developed by Laser Soft (1989) and released in the U.S. by NEC
Mega Drive version titled SD Valis developed by ISC note though published in Japan under the Laser Soft label (1992) and released in the U.S. by Renovation Products as Syd of Valis — Features Super-Deformed graphics.
Mega Drive version developed by Renovation Game (1990) and released in the U.S. by Renovation Products
PC Engine CD-ROM version developed by Laser Soft (1990) and released in the U.S. by NEC
PC Engine CD-ROM version developed by Laser Soft (1991)
Super Famicom version titled Super Valis: Akaki Tsuki no Otome developed by Laser Soft (1992) and released in the U.S. by Atlus as Super Valis IV
Alas, Poor Villain: Every game except the 4th one has one of these. Yuko mourns Reiko after killing her in the 1st game, and the Big Bads of the 2nd and 3rd games each using their dying words to explain their sympathetic motives to Yuko after she defeats them. All the bad guys in the 4th game are Card Carrying Villains, and are sliced and diced with impunity.
Dark World: The actual name of one of the lower realms in the Valis cosmos, along with the Dreamland and The Real World.
Deadly Upgrade: According to Nazetti in the third game, the price for releasing the Valis blade to its full power. It sucks that this also ends up being entirely cosmetic, albeit awesome.
Denial of Diagonal Attack: In the Genesis version, most of the sword powerups shoot horizontally. The exception is the one that produces homing arrows, and some powerups upgraded to level 3.
Evil Counterpart: Reiko becomes the Dark Valis Soldier to Yuko's Valis Soldier. Although after her defeat she does a Heel-Face Turn and appears in the later games Obi Wan Kenobi-style to advise or encourage Yuko
Evil Is Visceral: Emperor Megas has lots of twisted bundles of huge biomechanical arteries underneath his armor and face.
Inconsistent Dub: So is it Cham or Char? Valis, or Varis? Syd of Valis renames Yuko to Syd in game, but the box and manual disagree.
Jump Physics: In the Genesis version of Valis, Yuko can slide across a gap that she'd otherwise fall down.
Kick the Dog: Megas in Valis II's Sharp X68000 version. He's said to have killed his entire family, "including the women and children", his own underlings, and even the monsters who unsealed him- and that's just how he treats his allies.
Nintendo Hard: The third game after Yuko's deadly upgrade, arguably. Especially the Slippy-Slidey Ice World, which requires you, at one point, to jump on a moving platform (still slippery), quickly duck to avoid the suddenly low ceiling, and then use a well timed slide maneuver to get over a Pit Of Doom. And then you have to fight the boss.
Also, the fourth game (very hard to find that fourth game).
The first Valis is this all on its own, to the point where the Fan Translation has an optional easier version.
Panty Shot: The PC-Engine CD version of Valis 1 does this whenever Yuko jumps.
Robe and Wizard Hat: Valna, the one who fights using a magic spell, wears a robe (though not a hat).
The Chosen One: Yuko (and later Lena) are the ones who can save the world by wielding the Valis Sword.
Sailor Fuku: Yuko wears a sailor fuku for the first few stages before getting her Chainmail Bikini. The blue skirt matches the color of her hair. It returns in Valis II as one of her selectable outfits (she can switch it for a blazer in the Japanese computer version).
Saving the World: Of course the plot of the three games; subverted in the third game in that, by saving your world from the invading armies of the Dark World, you doom the inhabitants of the Dark World, which is slowly being swallowed into the void.