Hope this vid helped you! If you need a guide specific to your weapon, I've compiled a list of resources below. I'll update the list over time as more content is made. @Kiza_ has made vidoes for all melee weapons (called Melee cycle), where he comments his thought process while fighting Fatty. I recommend you watch those first, and then Openings if you wanna learn how to punish more openings.
Compilation of runs with pre-Fatalis gear (no commentary)
https://youtu.be/Y3rsedKaRus
*Great Sword*
Melee cycle: https://youtu.be/cXod7_ru8hA
Openings: https://youtu.be/Wzr0S9pAmXs
Openings extension: WIP
*Long Sword*
Melee cycle: https://youtu.be/KAl6BHGhToI
Openings https://youtu.be/VHQKlIeULKo
Openings https://youtu.be/yWRktpbcBZg
*Dual Blades*
Melee cycle: https://youtu.be/k7TYwKUqADQ
Openings & Builds: https://youtu.be/ynywmjsEw6s
*Insect Glaive*
Melee cycle: https://youtu.be/kNB2XALsfOc
Openings by https://youtu.be/2rcCNQJp04M
*Hunting Horn*
Melee cycle: https://youtu.be/URrdWizq4_4
Openings: WIP
*Hammer*
Melee cycle: https://youtu.be/_qkiMN3TMSk
Openings: WIP
*Switch Axe*
Melee cycle: https://youtu.be/ZeE_7VfpBm4
Openings: WIP
*Charge Blade*
Melee cycle (SAED style): https://youtu.be/o7hQpHUA1nY
Openings: WIP
*Sword & Shield*
Melee cycle: https://youtu.be/XY25c_jFD6Q
Openings: WIP
*Lance*
Melee cycle: https://youtu.be/OJQHE8qPAfs
All rounder guide https://youtu.be/-64qtN-tV9c
*Gunlance*
Melee cycle: https://youtu.be/BK3Gpopkzc8
Openings https://youtu.be/OmIRsBKFACk
*Bow*
All rounder guide https://youtu.be/k2CJS-Y2jKQ
Headbreak Guide https://youtu.be/F5uOvhbZEu0
*Light & Heavy Bowgun*
WIP
Chapters
00:00 Intro
01:26 Overview
01:55 Fireballs
03:18 Forward Flame
03:33 Zigzag Flame
03:59 Flame Shower
04:20 Line Explosion
04:47 Slaps
05:15 Cone
06:55 Tail Sweep
07:19 Charge
08:46 Bodyslam
10:41 Bites
11:12 Tail Slam
11:38 Fire Sweep
12:26 Charged Fireball
14:05 Canon Platform
14:44 Shelter
15:22 PHASE 2
15:33 Phase 2 Changes
16:35 Fire Puddle
17:11 Back Jump Fireball
17:41 Aerial Attacks
20:04 Dragonator Platform
20:42 PHASE 3
20:58 Phase 3 Changes
21:18 Triple Charged Fireball
22:24 Pin Attack
23:39 Side Flame
24:23 360 Fire Sweep
25:24 EXTRA STUFF
25:35 Surviving P3 Nova
26:39 P3 Nova Opening & Position
29:48 Roars
30:40 Smoke Bombs
32:51 Ground Knockdowns
33:47 Aerial Knockdowns
34:04 Paralysis
34:28 Sleep
35:03 Binder
35:57 Mounting
38:05 Dragonator
38:39 Outro
Music Credits:
Hide and Shoot by Soundridemusic. Link to Video: https://www.youtube.com/watch?v=i-NoU5Sedyw&t=0s
Simian Segue - Donkey Kong Country. Restored by Jammin' Sam Miller https://youtu.be/DTLfV7Ru5VY?si=0RdBOtPoj5xem7sr
No More What Ifs - Persona 5 Royal https://www.youtube.com/watch?v=7Ebf9PiGZFo
初詣 - Persona 5 Royal https://www.youtube.com/watch?v=db3ppIfP8ms
Fall theme - Harvest Moon: Magical Melody https://www.youtube.com/watch?v=TuFJF3TvOyA
Reminiscence About the Land - Monster Hunter 2 https://www.youtube.com/watch?v=P2FlfZyjerE&t=28s
Invitation from the Guild - Monster Hunter 3 https://www.youtube.com/watch?v=6F1boC0iY6g
File Select - Shantae and the Pirate's Curse https://www.youtube.com/watch?v=wB6oy6sH4lg&t=5s
Apotos (Day) - Sonic Unleashed https://www.youtube.com/watch?v=kmC6OImeNXY
Happy Holiday/Tokyo Xanadu Original Soundtrack/Copyright© Nihon Falcom Corporation https://www.youtube.com/watch?v=6vokpNeFOlQ
Setting Off/The Legend of Heroes VI: Sora no Kiseki FC Original Sound Track/Copyright© Nihon Falcom Corporation https://www.youtube.com/watch?v=F7Lh7RlJVC0
Sophisticated Fight/The Legend of Heroes VI: Sora no Kiseki FC Original Sound Track/Copyright© Nihon Falcom Corporation https://www.youtube.com/watch?v=Um5EbReY7rA
Tornado Defense (1st Battle) - Sonic Unleashed https://www.youtube.com/watch?v=lCaJJwgeL1s
A Moment of Rest - Monster Hunter 3 https://www.youtube.com/watch?v=UDSbxRyeFLQ
Strepitoso Fight/The Legend of Heroes: Sora no Kiseki SC Original Sound Track/Copyright© Nihon Falcom Corporation https://www.youtube.com/watch?v=onogsnnLe2o
Kokoto Village Theme - Monster Hunter https://www.youtube.com/watch?v=rYvZ-cNU1gc
Kitchen Theme - Monster Hunter: Freedom Unite https://www.youtube.com/watch?v=jK39vwlBpTw
Yearning for the Secret Hot Spring - Yukumo Village Theme - Monster Hunter Portable 3rd https://www.youtube.com/watch?v=CyKiahAL8aw
Maihoruku (Day) - Monster Hunter Frontier 2012 Anniversary https://www.youtube.com/watch?v=5nkS0VH5gpw
Elevator Music by Dar Golan https://www.youtube.com/watch?v=ezucNBvL_ac
Amusement Quarters of the Snowy Village - Monster Hunter: Freedom 2 https://www.youtube.com/watch?v=0-0hwqgRU2I
Village of the Sea, Moga - Monster Hunter 3 https://www.youtube.com/watch?v=rBBhBI_Tna4
Funny Quirky Comedy by Redafs.com, Licensed under Creative Commons: By Attribution 3.0 License https://www.youtube.com/watch?v=8MgA3SUwFHc