Before you even attempt the Fatalis quest, you should try and hit these MR levels to unlock helpful gear.

MR 70 - Silverlos armor (important for elemental weapons), Goldian armor (Divine Blessing secret) Challenger Charm 3

MR 100 - The minimum rank you should realistically fight Fatalis at. Unlocks augments for rarity 12 weapons and armor.

MR 150 - Temporal Mantle+

Album of General Recommended Builds[imgur.com]

If you can't build these sets exactly, just take note of these skills.

WEAPON AUGMENTS
- Health: Gives you lifesteal, synergizes very well with offensive skills.
- Affinity: Better than attack augment if you can't reach 100% affinity otherwise
- Attack: More damage if you already are capped on affinity
- Element: More damage for bow and dual blades

OFFENSIVE SKILL PRIORITY
1. Weakness Exploit
2. Critical Boost
3. Agitator
4. Critical Eye
5. Attack Boost

DEFENSIVE SKILL PRIORITY
1. Health Boost 3 (mandatory)
2. Divine Blessing (ONLY WITH DIVINE BLESSING SECRET FROM GOLDIAN ARMOR)
3. Evade Window

UTILITY SKILLS
- Any weapon specific skills
- Clutch Claw Boost
- Heavy Artillery (Make sure it's not just 'Artillery')
- Flinch Free (MANDATORY IN MULTIPLAYER)

Note that Fatalis is immune to stun.

Should you even bring your palico to the Fatalis hunt? Here are some pros and cons.
PROS:
-Gadgets can slightly tip the fight in your favor
-Palico can take aggro off of you
-Can apply a status effect (paralyze is best)

CONS:
-Will make some tactics impossible or difficult, such as smoke bombing or cone baiting
-Fatalis will become more unpredictable when targeting palico

Ultimately, bringing your palico will come down to personal preference.

Palico Equipment:
Armor literally doesn't matter for your palico, just choose whatever you think looks nice.
I recommend a status effect weapon for your palico as it's pretty good at proccing status ailments, and paralysis works well for both solo and multiplayer.

Against Fatalis, every second counts! You simply do not have the time to be chugging down a mega potion, or similar. Therefore, it's important to bring items that are quick to use and highly effective.

Max / Ancient Potions and materials to make more
Great Sushifish Scales (Heals about 1/2 HP instantly)
Whetfish Fin+
Smoke Bombs and materials to make more
Farcaster
Power/Armor Charms/Talons
Mega Demondrug
Might Seeds

Do note that Fatalis is immune to flash pods.

DO:
-Position yourself close to and in front of Fatalis whenever possible
-Focus head and chest, as they take the most damage
-Be patient above all, learn Fatalis' attacks and how to punish them

DON'T
-Use the cannons at all
-Spam Dragon Pods to flinch Fatalis
-Mount Fatalis in multiplayer

Beginner Guide by myself, goes over the same stuff as this written guide in long form.

Bow Guide by Tidus69

Shoutout to the Monster Hunter Hub Discord: https://discord.gg/UShSTfWe