Board Thread:Questions and Answers/@comment-38889494-20190322121715/@comment-32182236-20190322130724

It depends on how you count.

If we just count all the monsters we've seen, that weren't killed, we get Bratty and Catty, Gerson, Nice Cream Guy, Snowdin Shopkeeper, Alphys, Monster Kid, Grillby, Napstablook, Faun, Snowman, two Innkeepers, a Rabbit Girl and Cinnamon, Gift Bear, Politics Bear, Scarf Mouse, Nacarat Jester, the three members of the Slime Family.. Okay, I should probably stop trying to list them all. It's 71.

If we add the 5 Amalagamates you battle in True Pacifist (sure, you don't SEE them in Genocide, but they're still there), plus the four that corner you before Alphys shows up, and another one that tucks you into bed, you get a total of 81 monsters. But we're still missing the lone spider that we see in Muffet's battle. Make that 82. Take into account that you can't encounter Glyde or So Sorry, and that boosts the number again to 84.

But we know there has to be more than that. How? By counting the SOULs that we see surround Asriel as he breaks the Barrier, we can deduce that at least 322 monsters exist. The most monsters you can possibly kill is 120 (presuming you plan it out perfectly.. And this includes Chara's kills up until the world ends), so at least 202 monsters survive. However, you can also only kill 105 monsters (including the ones Chara kills), so in that case, at least 215 survive.

But there's yet another method of counting. It's possible to get the same monster again and again, and fulfill the count that way. This, and the ability to get multiple monsters to appear even when there's only "1 left", implies the kill count marks the point where monsters evacuate-NOT the point where you've actually killed everyone. Given this, we can actually presume that there are 20 of each Ruins random (non-unique) encounter monster, 16 of each Snowdin random (non-unique) encounter monster, etc. We then add one monster to the total for each unique encounter.

If we count this way (of course, subtracting the amount that actually does die), we get 100 in the Ruins, 35 in Snowdin (most encounters are unique ones), 73 in Waterfall, and 280 in Hotland/CORE, giving us a sum of 488 monsters. Add that to the number of monsters we already know we can't kill from our first total, and we get 572 surviving monsters.

Oh, and if the annoying dog counts as a monster, it's 573.