Self-Explanatory. Since some monster stats have variation, I'll opt for the bigger stats ('cause usually that's when a monster's willing to fight, with some smaller exceptions, like Undyne, for example).
Beings like Flowey/God Flowey or Gaster have never shown their stats, or at least have the "stat" option, i n - g a m e. So I won't put them bellow.
Hotland and Core:
Extra: The Humans
- Toriel is the strongest monster in the Ruins.
- Papyrus is the strongest monster in Snowdin.
- Undyne is the strongest monster in Waterfall.
- Muffet is the strongest monster in Hotland.
- Mettaton EX is the strongest monster in the Core.
- Both Asgore and Toriel are superior to most monsters.
- Asriel is the strongest being in the Underground via stats.
- Most monsters are glass cannons.
- Undyne's DEF in faux battle is actually higher than in the battle itself. Even though her's attacks are weaker.
- Both Asgore and Toriel (80ATK 80DEF) are stronger than most monsters, but they are weaker than Mettaton NEO (90 ATK 9DEF), Undyne the Undying (99ATK 99DEF) and Asriel Dreemurr (∞ATK ∞DEF)
- Despite being weaker than Monster Kid (2ATK 2DEF), Sans (1ATK 1DEF) still being tougher than the Dummy (0ATK 0DEF), Glad Dummy (0ATK 0DEF), Jerry (0ATK 30DEF) and Snowdrake's Mother (0ATK 0DEF).
- The strongest monsters are: 1.Asriel Dreemurr, 2.Undyne the Undying, 3.Mettaton NEO, 4.Asgore & Toriel.