After all this time, I'm glad to present my complete guide to get all achievements in Disbelief Papyrus (by Cezar Andrade).
Achievement list :
0:00 SPOILER WARNING
0:12 Genocide Ending
1:23 Good Ending
2:47 Remorseful Ending
5:36 Betrayal Ending
7:56 Invalid Ending
11:27 Be captured by Papyrus
12:20 Hide five consecutive times
17:17 Defeat an Egg Dog
19:39 Check all enemies
21:54 Flee in all occasions
25:32 Play with Papyrus' life
27:00 NO ITEMS
27:37 Judge the Cold Spaghetti of Papyrus
31:31 Die in the style of Minecraft
32:19 Challenge Undyne then do a NO HIT
33:23 Trophy !
33:39 NO HIT phase 1
36:44 NO HIT phase 1 to 4
36:55 DON'T YOU DARE
38:39 Random events - explanation
39:09 Double Trouble
40:38 Keep going, Don't give up
41:26 Beware of the DOG !
43:27 Papyrus misses his brother so much...
44:18 SOMEBODY TOUCHA MY SPAGHET !
44:51 How did that thing run away ?!
45:28 Hit Sans
46:14 Die during your turn
Disbelief Papyrus - Full fight [NO HIT] : https://youtu.be/-UWMptN1xfs
Spoiler-free version of this guide : https://www.youtube.com/watch?v=rW3WCO5zDaE
This game is a CYF mod that you can find on Game Jolt : https://gamejolt.com/games/DisbeliefUnofficial/464116
~~~~ CREDITS ~~~~
Mod by Cezar Andrade
Based on the animation of FlamesAtGames
Sprites : LuckyStudios, Lone, FlamesAtGames
Undertale by Toby Fox
Music :
Interstellar Retribution - DBOYD & KOMMISAR
Phase 2 / But The Earth Grew a Spine - JimmyTheBassist
Backbone - Lone
Final Chance - FlamesAtGames
Megalo Strike Back Lullaby - Lia1291 / Sapph
Bonetrousle / Megalovania Piano - Chrystal Chameleon