Press M to swap the Knight for Super Mario 64's real Mario, anywhere you can move freely. Press M again to get the Knight back.
His real SM64 moveset in 2D: momentum running, single, double and triple jumps, backflips, side flips, long jumps, wall kicks, dives, slide kicks and ground pounds, on Hallownest's own floors and walls.
Punches and kicks hurt enemies through the game's own nail hit, so they flash, recoil and die as usual. Damage scales with your nail.
Your masks are Mario's health. The game's own damage, invincibility and death stay in charge; cutscenes, benches and doors still belong to the Knight.
Single player.
You need: Hollow Knight (Steam) and your own Super Mario 64 (US) ROM. Melty finds it and prepares it when you press Play. Nothing from either game is included.
Credits: libsm64 by jaburns and contributors (CC0); bindings and ROM loading adapted from Mario 64 Survivor (MIT). Hollow Knight by Team Cherry, Super Mario 64 by Nintendo.