Luke Maker

So, starting with the world, it would follow the basics of undertale, but heavily focused on puzzles.

The Royal Guard members would be Royal Scientist devoted to make weapons and creating ways to defeat humans, some would use puzzles, others would use robots or even improve their bodies with science.

Most regular monsters would give riddles, puzzles and things that test your mind in general instead of the usual fights.

The usual puzzles from room to room would be much more deadly like the lasers we see in the final stages of the game.

As for the main monsters that are treated as area bosses (or something similar), I will give a resume about them:

Toriel would be one of the few people to not rely on puzzles nor machinery but her magic alone would be used in such smart way that dodging her attacks could be considered a puzzle by itself;

Papyrus would be a brilliant Royal Scientist, but he was unable to join as a official member, the reason? He would be focused way too much in doing traps (which is not his specialty) instead of Puzzles that is what he excels at... his traps would be very non-letal, showing both his incompatibility with the method and his naivety;

Undyne as a member of the Royal Scientists would develop a variety of melee weapons with special properties, she would not be as strong as her original counterpart but she would use special armor to make up for it, you can think of her like a technological Erza Scarlet;

Alphys would be the creator of the armor Undyne uses, her monster chimeras not only would be way more stable but would also be the Royal Guard of this AU, because of that she does not to work as much anymore, resulting in something similar to what we see in the game;

Mettaton would be another member of the Royal Guard of this AU, being way more combat focused with samurai-like swords, Alphys would pretty much design Mettaton with her anime mindset and instead of the TV shows, Mettaton would do vlods of the daily jobs and similar stuff, mainly focusing in being something similar as a youtuber;

Asgore would be very similar to Toriel in the meaning that his magic and attacks would almost act as living puzzles. Before fighting him Frisk would have to travel a entire room made of traps using Asgore's fire magic, all of them being very letal;

For Asriel/Flowey there's no need to change his focal points, only difference being he was unable to stay determined due to Sans being even more aware of timeline changes and directly fighting against him;

Sans would be the most different one, as a ex member of the Royal Scientists he had direct contact with the first human to die there after Chara and would later be responsible for doing experiments related to human souls, resulting on him absorbing the soul of the same human he had contact with in the past. The reason why his design was full of stars is because that human would share the same love of stars that the monsters who live in the underground have.

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