Koumajou Densetsu (AKA: Legend of Scarlet Devil Castle, 紅魔城伝説 緋色の交響曲, こうまじょうでんせつ あけいろのこうきょうきょく) is a series of independent (fan-made) games inspired from Castlevania developed by the fan club Frontier Aja from Japan. It can be seen as the fusion of KONAMI's Castlevania series and Toho Project's (AKA: TouHou Project, 東方プロジェクト, Touhou Purojekuto, Project Shrine Maiden) series of doujin games.

If you find you have become interested in that kind of retro cave exploration game with very high difficulty coefficient after playing Spelunky, then La-Mulana (ラ・ムラーナ) will be another good play for you.

VVVVVV is a challenging gravity-based action puzzle game with 8-bit and fantastic styles. Your goal is to explore and escape from this mystical world through adventure.

Akuji The Demon (魔王のアクジ) is a classic side-scrolling small indie game from Japan, whose pixel and lovely styles are very similar to the "Cave Story". In many similar games, players are always playing the hero, but in Akuji The Demon you will be a big villain.

Terraria is a popularity pixel-style indie game nicknamed the 2D side-scrolling edition of the famous sandbox game Minecraft, which was launched on PC in as early as 2011. But personally I thought it was just in terms of its randomness and pixel style, for the game system design it was inspired most from the Clonk Rage. Of course, it's really as fascinating as Minecraft.