Valis SD (ヴァリス SD, Varisu Esu Di), known in America as Syd of Valis (literally, Super Yuuko Deformed of Valis) is the first spin-off game of the Valis series. The game's plot is mostly built upon the events of Valis II, parodying them with an SD (Super Deformed) style in the characters' designs, making them look funnier and greatly exaggerating their attitudes.

This game has basically the same gameplay as any other Valis game, but there are many differences. To start, Yuko is slightly faster here than in the other games. She has the same power-up attack items from Valis II available to her, as well as the multiple suits that she has in the MSX and PC88/98 versions of that game. She wins them by beating mini-bosses and/or bosses. Depending on the suit, her attack, defense and speed stats will change. Finally, there is a scoring system that, as in Valis II, will give the player an extra life for each 10000 points earned.

Yuko also has some new abilities that are exclusive to the game. These abilities include double jumping and shooting upwards. She also recovers her HP bar by beating bosses and sub-bosses. She can't die automatically by falling into holes, but simply loses HP, making the game easier.

In comparison to Valis II, the game has different music and level structures, though the level backgrounds are identical.