Undertale: 10 Hardest Boss Fights, Ranked 1 Sans. The most iconic character in Undertale has an equally iconic fight. 2 Undyne (Genocide) ... 3 Photoshop Flowey. ... 4 Asgore. ... 5 Muffet. ... 6 Mettaton. ... 7 Undyne (Neutral/Pacifist) ... 8 Mad Mew Mew. ... More items... Apr 3, 2023