Warren Spector considered Ultima VI: The False Prophet (1990) the first game to have an immersive sim mentality as while played from an top-down view, it relied less on events and planned-out puzzles, and instead provided the rulesets and systems through its living world to allow players to craft their own solutions to situations. Spector described one playtesting example from Ultima VI that he considered the genesis of the immersive sim genre, in which a playtester lacked a magical spell needed by his party to pass by a closed gate, and instead used a pet mouse character to sneak through small spaces and access the necessary controls to open the gate, something none of the developers had anticipated.