This game was released in October of 1986. Two months earlier, in August, Metroid was made available in Japan for the Famicom Disk System. In September, and also for the Famicom Disk System, Akumajou Dracula – aka Castlevania – was, as well, released in Japan. So, unknowingly, The Sacred Armor of Antiriad gave birth to the metroidvania subgenre.
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Antiriad, the very first Metroidvania [1986, C64 / CPC / ZX Spectrum] - It's a Pixel THING - Ep.#61