I thought you were talking about the boss named dummy marota, not the genocide route thing. The save I gave is just inside the cow vtuber's room in the normal game. I don't actually have a save for Lust Grimm Dummy on hand, but here is the guide:
LustGrimm Dummy has much less content than the normal game: most of the world is distorted and inaccessible, enemy attacks instantly defeat the player and cause a Game Over, and almost no H-scenes are available. The genocide route requires the player to play both this and the normal game.
In the normal game,
the player needs to collect at least 60 Red Riding Medals, listen to the Grimm Radio on the frequency 666, and talk to at least six of a certain set of succubus NPCs (who appear when the player has obtained Brave victories against certain bosses on the highest difficulty, Real); finally, they must save the game in
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: Outskirts. They must transfer this save file to
LustGrimm Dummy and load this save file.
Speaking to Hatter and answering "Yes" to her question transports Magrut to a strange area with green platforms and Vigor-draining succubi. While going through this area, Magrut will learn the Hatter and
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have come to this world to investigate something. At the end, the Hatter warns Magrut of a powerful devil sealed here and tells him to forget everything he's seen just now.
Meeting Demon
Magrut then returns to the previous world. If he then examines the sign here repeatedly, it will ask if he desires the future's end and ask him to hand over power. Doing so transports Magrut to the sealed
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, who explains how she was sealed and wounded by her most hated enemy, but his power will let her escape and send that enemy into despair. The player is offered a choice of submitting to Demon or quitting the game, but regardless of what they pick (even if they manually close the game window), Demon overwrites every save file and and drains Magrut's power with a titjob. The title screen is now altered to show just the word "Again" and a distorted, red view of Demon's face.
The save I provided has some of the bosses beaten with brave conditions, and I think it has 60 medals as well, so if you really want you can check the achievements and do the extra content.