All of the Mario content for Minecraft:

Mod: Retro64 (github, Curseforge) by dylanpdx (twitter, Curseforge)
The star of this modpack. Provide a Mario 64 ROM of your own and you can play Minecraft as WAHOO himself, complete with backwards long jumps.
The mod is still a work in progress with a beta in dev for 1.20. Now it's for 1.18.2 & 1.19.3 on Forge, or 1.19 on Fabric. 1.18.x has the most Mario-themed mods and resource packs so All The Mario is on 1.18.2.

Resource Pack: Super Mario Craft by the_jumper_99
Textures, music, mobs, and more! Gives the world a new but familiar look.

Resource Pack: Super Mario Texture Pack by MrTutankhamun
Turns the leather armor into Mario’s clothes, among other changes.

Resource Pack: Super Mario Maker Texture pack by BuilderGG
Some nice chunky blocks.

Resource Pack: All The Mario Resource Pack by Tramplin' Stu (that's me!)
Custom graphics and fixes for this mod pack.

Mod: Mario Games Pack by Floppicus
New tabs, blocks, items, pipes, weapons, and tools!

Mod: bart's funny version of mario & luigi dreamstone (Curseforge, Modrinth) by bartb6 (Curseforge, Modrinth)
Adds new items,endgame gear, and a new ore tier from Mario & Luigi Dream Team. 

Mod: Mega Mario by SWDTeam
Adds the Mega Starman effect from Super Paper Mario, with destructive implications. 

Mod: Super Mario Stuff by FnafyyBoyy
Coins and pipes. 
Dependency: geckolib

Mod: Mario 64 Paintings by Licit_Lettuc
Adds 10 new paintings in multiple sizes.

Resource Pack: New Super Mario Bros U Deluxe by Emilybear6046
Replaces paintings with official art and screenshots from NSMBUD and NSLU. 

Resource Pack: Paintings Into Retro Games by Kulhat
Replaces some paintings with NES game screenshots.

Resource Pack: Mario Music Pack by Jke-Jr
More lovely Mario music. See page for track list. 

Gameplay & Quality of Life:

Xaero's Minimap & Xaero's World Map by thexaero
In-game map and mini-map.

FTB Quests & Teams by FTB
Quest book & Multiplayer support.
Dependencies: FTB Library, Architechtury & Item Filters

Mod: Controllable by mrcrayfish
Play with a controller using analog movement. Provides Steam Deck support.

Ceiling Torch by bl4ckscor3
Place torches on ceilings.

FallingTree by Rakambda
Axes fell trees under a certain size. 

Just Enough Items by mezz
Better recipe viewer.

Jade by Snownee
Tells you what you're looking at.

Mouse Tweaks by YaLTeR
Mouse shortcuts.

Inventory Sorter (Configurable) by qyurila
Sort Inventories.

Polymorph by TheIllusiveC4
Solve recipe conflicts with bottom to switch between results. Might not actually be needed in this pack.

Controlling by jaredlll08
Description: Keybinds are now searchable.

Let Me Despawn by frikinjay
Description: Enemies despawn better.

Let Me Sleep - Better Sleep Check by TwinSouls
Description: Enemies must have aggro to interrupt tucking in.

Bed Is Never Too Far Away by AMDYep
Sleep in further beds.

Calm Mornings by TwinSouls
Waking up despawns nearby enemies. 

Transmog by Hidoni
Make your favorite things look like other things.

I Know What I'm Doing by HeckinChloe
Removes Minecraft tutorial messages.

Followers Teleport Too by Serilum
Depedency: Collective
Pets join you when teleported via command.

Just Enough Breeding (JEBr) by Christofmeg
Displays more mob and item info in JEI.

Better Brightness Slider by LaidBackSloth
The brightness slider now goes from -100% to 1200% instead of 0% to 100%.

Experimental Settings Disabler by Eruannie_9
“Disables the experimental world icon, generation and loading warning settings.”

Bigger Stacks by thanksihadtosignupfo
Item stack limit increased to 999.

Haven Growth (shift / twerk / sprint to grow plants and crops) by CathieNova
Accelerate plant growth, but you have to work for it. 

Trample No More by DarkhaxDev
Plants are safe from platforming.

Sneak Through Berries by Trikzon
Take it slow and don’t take damage from berries.

Just Another Rotten Flesh to Leather Mod by alexdaum1
A better use for that garbage skin.

Just Enough Resources (JER) by way2muchnoise
Find where items occur naturally.

Just Enough Professions (JEP) by Mrbysco
How to train your Toad. 

Auto Planting Forests by Lothrazar
Saplings that would despawn plant themselves. 

Just Zoom by Keksuccino
Look far away with a hotkey.

Easy Villagers by henkelmax
Pick up Toads and put them in your pocket.

Villagers Respawn by MacTso
Toads with beds die hard. 

Open Loader by DarkhaxDev
Always use the correct load order for resource packs.

It’s the Little Things by Zlepper
Welcome screen and game icon. 

Tips by DarkhaxDev
Loading Screen Tips

Enigmatic Graves by Quarris, Mute_Tiefling, Ridanisaurus, and NillerMedDild
Items dropped on death are safe.

Movement:

Jumpy Boats by LobsterJonn
Hop in boats.

Jump Over Fences by kreezxil
Jump over fences.

Grappling Hook Mod by yyon
Grappling Hook for Steve and Alex.

Wall-Jump TXF by jahirtrap
Expanded moveset for Steve and Alex.

StepItUp by spoorn
Steve and Alex step up 1m blocks. Configurable.

Useful Slime by MincraftEinstein
Classic movement tool for Alex and Steve.

Softer Hay Bales by Serilum
“Hay bales negate fall damage entirely, Assassin's Creed style.”

Parrochute by Eugene2000
Take to the skies with actual birds.

Tools:

Useful Hats by cech12
New hats with special powers.

Wooden Hopper by cech12
Hoppers for cheaper. Be careful not to use too many of these.

Golden Hopper by MrCrayfish
Basic item sorting. Be careful not to use too many of these.

Wooden Shears by cech12
Shears for cheaper.

Waystones by BlayTheNinth and Xaero's Minimap & World Map - Waystones Compatibility by precise.modpacker
Get around.

Curios API by TheIllusiveC4
*slaps roof* you can fit so many equipables in this bad boy.

CERBON's Better Totem of Undying by CerbonXD
Wear totems in a curio slot and free up your offhand. 

Void Totem by Affehund
Don't fear the void. 

Vein Mining by TheIllusiveC4
Vein mining is an enchantment. 

Crafting on a Stick by ofek
Craft on the go.

Vanilla Zoom by Serilum
Reveal enemy health and look even farther with the spyglass.

Passive Shield by Serilum
Off-hand shields work without activating them.

AstikorCarts [Horse Carts] by issork
Take your things with you in a self- or yoshi-drawn wagon.

JustHammers by ErrorMikey
A new set of more effective mining tools. 

Nature's Compass by Chaosyr
Find your favorite biomes. 

Biomes In Jars by keksuccino
Bring your favorite biomes with you.

Explorer's Compass by Chaosyr
Find your favorite structures. 

MiniGames N ParkourBlocks+ by TurtLeLaaG98
Fun things to jump on. 

Comforts by TheIllusiveC4
Sleep the days away.

Magnum Torch by Fuzs
Light and monster-proof a wide area.

Fireproof Boats by LobsterJonn
Another option for lava lakes.

Rings of Ascension by focamacho
Powerups you can put on your hands.

Bed Benefits by Darkhax
Beds heal and reset potion effects.

Sophisticated Backpacks by P3pp3rF1y
Carry an insane amount, feed yourself, and more across 5 tiers of storage. Placeable wearable powerful chests. Dependency: Sophisticated Core

Iron Chests: Restocked by ThatGravyBoat
We have powerful chests at home.

Iron Furnaces by XenoMustache & Pizzaatime
Why wait when you could build increasingly powerful furnaces?

Portable Tanks by Dremoline
Bring more of your favorite liquids.

Botany Pots by DarkhaxDev
Botany Trees by DarkhaxDev
and
[BPOP]Botany Pots Ore Planting by mango_buff
Grow more than just ores at home with botany pots.

Capsule by Lythom
Put your base in your pocket.

Mob Capturing Tool by matyrobbrt
Put mobs in your pocket.

Wormhole (Portals) by SuperMartijn642
DIY portals.

Uncrafter by ketheroth
Reclaim some ingredients.

Construction Wand by ThetaDev
Quick and efficient building.

Tempad by terrariumearth
The ultimate personal teleportation tool.

World Generation:

Oh The Biomes You'll Go by JT122406
Biomes O' Plenty by Forstride
William Wythers' Expanded Ecosphere by Cristelknight
Regions Unexplored by UHQ-GAMES
YUNG's Cave Biomes by YUNGNICKYOUNG
Cherry Blossom Grotto by Dekunutter
New biomes to explore.

Immersive Caves by herculuke
Terralith by Starmute
Overhauled world generation math.
Dependency: Cristel Lib by Cristelknight

TerraBlender by Adubbz
Combine all previous enviromental mods.

Towns and Towers by Biban_Auriu
ChoiceTheorem's Overhauled Village by ChoiceTheorem
and
Underground Villages by Mrbysco
Cooler towns. 

Berries Resources by ">" rel="nofollow">fori
Oreberries Replanted by Mrbysco
and
Metal Bushes (Forge) by DaveInTime
Berries are more useful. Grow ores at home.

Broglis Plants by broglii
New plants with bite.

YUNG's Bridges by YUNGNICKYOUNG
Run and jump past some rivers.

Villager Names by Serilum
Toads have names.

In Control! by McJty
Adjust and block certain mob spawns.

Initial Spawn Dimension by SecretAsian
Allow spawn in other dimensions.

Fixes & Optimization:

Cull Less Leaves Reforged by CCr4ft3r
Entity Culling by tr7z
FerriteCore by malte0811
Icterine by Mephodio
Not Enough Recipe Book [NERB] by SSKrillSS
Radium Reforged by Asek3
Smooth Boot (Reloaded) by AbdElAziz

Graphics & Visuals:

These mods combined replace OptiFine:
[EMF] Entity Model Features by Traben
[ETF] Entity Texture Features by Traben
Connectedness by Asek3
Reforgium by Asek3
Rubidium by Asek3 
TexTrue's Rubidium Options by TexTrue
Embeddium (Rubidium) Extra by dima_dencep

Drippy Loading Screen, Konkrete and FancyMenu by keksuccino 
This enables custom loading screens and menus.

Make Bubbles Pop by Tschipcraft
Bubbles pop.

Immersive Paintings by Conczin

Maps & Levels:

Peach's Castle by Ambrose1810
Parkour Civilization by tunky67 & Luc1dw0IF 
Parkour Mountain 2 by Teddyishappyl
Parkour Spiral by Hielke
The Spiral Parkour by Blayanek
Great Biome Explorers by SilverfishStone
Ancient Greek Temple by Daskalos
Mashup: PC Edition by 4J & furtas
Crafted Kingdoms by daninator08
Glacial Auroras by Potasiumola