Underfell Routes (My take)
The neutral route has the most ending so each one is very different but the basic cost is Frisk selfishly only saves themselves and escapes the Underground (some routes along with Flowey).
1. Teaming up with Flowey
2. Leaving or killing Toriel
3. Befriending, defeating, or killing Papyrus
4. Escaping or killing Undyne
5. Saving or Killing Mettaton
7. Fighting (if you have 1-5 LV) or being let go by Sans
9.Flowey absorbs the Human Souls to stop the protagonist from leaving everyone behind without trying to save them
10. Fighting and either saving or killing Savior Flowey
11. Chara confronts you trying to sway you to do the freedom route now
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Convincing everyone to realize their flaws and work together for their freedom
2. Convincing Toriel she needs to learn to move on and handle her grief properly
3. Convincing Papyrus to reconcile with his brother
4. Date/Hangout with Papyrus where you convince him that he doesn't need to be a royal Gaurd to have lots of friends
5. Saving Monster Kid and convincing them that they don't need to act tough and mean to get people to be friends with them
6. Saving Undyne from dehydration and showing her not all humans are evil
7. Hangout with Undyne where you convince her that her pursuit of being the strongest has pushed away those she's cared about
8. Saving Mettaton from Alphys and convincing him that he's beautiful on the inside
9. Convincing Alphys that she's not the bad person she claims to be
10. Date with Alphys where you convince her to do the right thing and come clear about her mistakes. Also where Undyne proposes to Alphys
11. Discovering the True Lab and saving all the Tortured Souls (Amalgamates) and convincing Alphys to let them go free
12. Fighting Sans and showing him all the good things youve done and that everyone deserves mercy
13. Fighting and sparing when he tires Asgore much to his surprise and he apologizes to everyone for all the awful things he's done in pursuit of freedom
14. Flowey absorbs the human and monster souls convinced that when you make it to the surface you'll just reset and take away everyone's happy ending and becoming Asriel again
15. Saving Asriel by first saving the souls within him and then telling him that you are in this together Asriel then breaks the barrier freeing everyone
16. Chara confronts you and tells you that you can move on now and let everyone have their happy ending and tries to convince you not to reset
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Killing every monster you fight. Taking away the monsters hopes
2. Killing Toriel causing her to try and give up her soul to you but it's too weak
3. Killing Papyrus causing Sans to disappear for the rest of the game
4. Killing Undyne causing her to drop her ring she meant to give to Alphys
5. Killing Mettaton causing him to shut down all power in the Hell-Land and the Labyrinth
6. Killing Alphys causing her to attempt to blow up the Labyrinth in an attempt to take you down with her but Flowey helps you escape and now almost everyone in Hell-Land is dead
7. Sans lets you go like the coward he is to let you kill Asgore 8. Kill Asgore causing him to attempt to absorb the Human Souls but they all break
9. Flowey tries to stop you from leaving trying to question why you did all this
10. You kill Flowey by cutting off his stem and stomping on him
11. Chara confronts you and forces you to reset
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Genocide-Lost Control Route
Frisk fully gives up control to the player and kills all the monsters in the underground not just the ones the encounter but actively hunting down every monster possible
2. Killing all the monsters in the Catacombs and Toriel causing her to realize that you aren't her lost child or even human
3. Killing everyone in Coldtown and Papyrus causing him to regret not trying to make things right with Sans and Undyne
4. Killing everyone in Dark Seas including Monster Kid and the Undyne who become Undyne the Ever Dying. After killing her she warns you that Alphys has a plan to make sure you're gone for good before dropping the ring for Alphys
5. Flowey betrays you and tells you that you've gone too far and that he can't sit back and let this go on (this might be moved to before Undyne's fight)
6. Killing everyone in Hell-Land and the Labyrinth along with Mettaton.NEO who shuts down Hell-Land and the Labyrinths power
7. Alphys injects herself with determination she extracted from the Tortured Souls and turns in Tortured Alphys in an attempt to finally stop you. She can't be killed and you have to wait until she melts to nothing from too much determination 8. Sans fights you to get revenge and after he tires out you're able to kill him
9. Asgore fights you like normal (unaware of your murders) and is killed
10. Flowey attempts to stop you now and force you to reset but he fails
11. Chara confronts you and tries to force you to reset
