Which Undertale Boss is REALLY the Strongest?

There are a lot of strong monsters in the Underground... but which one is the strongest of them all? Thumbnail Art by Octigone: https://x.com/octigone Undertale Boss Fight Simulation Mod by Bluesheep3 and Per Undertale and its OST by Toby Fox and published by Materia Collective Discord: https://discord.gg/eJw3Cq3 Twitter: https://x.com/Mystic_Slime