Running away from your problems: A guide to Endless rushing

Introduction

This won't cover the basics of Endless, because it's really not that complex.
We're here to talk about rushing: the fastest and lowest-effort way to farm Endless.

Rushing runs work like this: You'll spend the first thousand floors or so setting up your carry for the rush, then you'll spend the rest using Run Away to flee every fight and Master Ball everything you want to catch. Read on for the specifics.

Starters

Due to current berry limitations, there's only one reliable Metal Burst strategy now: Sturdy combined with Poison Heal. This is now mandatory, as if you're running anything else then you are very vulnerable to RNG deciding your run is over.

First off, you're going to need to bring something with Sturdy as a passive. Squirtle is the recommended choice due to being strong enough to carry the game on its own on top of having access to a Gigantamax form. Gigantamax provides immunity to a sizable number of moves and effects that can mess with you, such as Flinches, Skill Swap, Roar, Disable, Encore, Destiny Bond, and more. For this reason, G-Max Blastoise is the optimal Sturdy mon. Other options are certainly viable, but expect to deal with more annoyances.

Next, you're going to want something with Poison Heal as an ability in your starting team as well due to how rare it is. Shroomish and Gligar have access to it, though Gligar's Immunity doesn't become Poison Heal until it evolves.

If you don't have a mon with Sturdy as a passive, you're better off just running Classic to grind candies and get Squirtle's passive. Trying to run without Poison Heal is a headache. Just go ahead and grind Squirtle candies.

Ideally one of the above mons will be strong enough to double as your Carry for the early game, such as Squirtle or Guts Shroomish, but if not then bring along a strong early game mon to fill the role.

For the rest of the slots, fill up on shinies and Pickup. Pickup is now mandatory instead of just good to have, as Berry Pouch is no longer infinite and the extremely low cap means you can't simply stock up early and then coast until the end. Your Metal Burster might not need berries, but your other mon(s) will.

The Team

Over the course of the early game, you'll be assembling the below mons. Take your time and do it right, there's no hurry and you'll likely finish this step before you're ready to rush anyway.

The Metal Burster

The guy who's going to be doing all the damage. This will be your Sturdy mon fused with your Poison Heal mon and needs to have the following moveset:

Metal Burst
Protect
Soak
Salt Cure

To get this set, use fusion to put Metal Burst, Soak, and Salt Cure onto whichever of the two mons you're not using as a Carry, then fuse that mon into your Carry when you're ready to rush. If you're using a third mon as a Carry, then combine the first two however you choose.

Metal Burst will be your main damage dealer, while Salt Cure adds some passive damage. Soak boosts Salt Cure, and Protect in conjunction with Leftovers, Healing Charm, and Poison Heal lets you recover to full HP between hits to allow re-use of Sturdy.

The Support

Backup damage support for the late game. It needs the following moveset:

Curse
Leech Seed
Gastro Acid
Protect

In addition to the above, this needs to be Ghost-Type and have Sturdy as an ability. How you put this together depends on what mons you start with and what you find in the run.

Curse and Leech Seed provide more passive damage, while Gastro Acid disables abilities like Mold Breaker that could ruin your day.

The Runner

This is a Ghost-Type with Run Away. That's it, that's all you need. Its moves don't matter, though you probably still want to put Protect on it just in case. Now that Ghost-Types can no longer be trapped, running one is optimal. Pick something with a sufficiently spooky primary type and fuse it with a Rapidash or something.

Early Game

Play it like a normal Endless run while you work on putting together the Support and getting the required moves for your Metal Burster. If you've done Endless before, which you absolutely should before trying to rush, you don't need an explanation of everything to do here.

There are a few things you want to do differently, however, so I'll list them here:

Get high stacks of both EXP Charm (Caps at 99) and Super EXP Charm (Caps at 30). Being at level cap is enough to keep Metal Burst relevant damage-wise, and the charms will let you keep up with the cap without spending shops on Rare Candies. You don't need to cap the stacks, but it doesn't hurt to do so.
Similarly, try and get stacks of Lucky Egg and Golden Egg to further increase EXP gain. You won't get far with Golden Egg stacks now, but grabbing them as you rush is never a bad move.
Candy Jar is mildly helpful while you're getting set up, but don't prioritize it. The point of rushing is to skip as many fights as possible, so you won't be getting many Rare Candies.
Get a large stack of HP Up on whoever will be the primary mon in your Metal Burster. Ideally this is 31, but if you want to start rushing before you reach 31 it's not a big deal.
Stock up on Master Balls while you can.
DO NOT TAKE EXP BALANCE UNDER ANY CIRCUMSTANCES. It kills your Metal Burster's EXP gain which is critical to a smooth lategame, so taking it is kneecapping yourself. It's not impossible to reach 5850 with it, but it's significantly more annoying.
Don't forget that your Support needs Leftovers too!

Switching

Once you've got all your stacks of Leftovers and Focus Band, as well a large stack of HP Up, use fusion to create your Metal Burster. Learn Metal Burst, Soak, and Salt Cure, while leaving a useful attack in the last slot.

Immediately after fusing, your number one priority is to roll a speed-reducing mint so that you can actually make use of Metal Burst. Once you have your speed-reducing mint, replace that last attacking move with Protect either by TM or by Memory Shroom if you brought Squirtle or Burmy. Transfer all stacks of Quick Claw and Multi Lens off your Metal Burster. You're all set to rush now.

Rushing

Put your Runner in the lead and start running from everything. If you see something you want, ball it. If you get trapped, ball it or kill it. Every 50 floors, you'll have to actually fight an enemy. For normal paradox fights, just spam Metal Burst. For Eternatus fights, apply your passive damage first and then spam Metal Burst.

If you run low on Master Balls or use a Reviver Seed, kill non-boss enemies to restock. They'll go down in a single Metal Burst.

And that's it! Repeat until 5850. Enjoy your shinies, HAs, vouchers, or whatever else you're doing Endless for.

Tech Options

The team above is really all you need to make it through Endless. However, there are some things you can add to help smooth double battles out a bit if you like. These are luxuries at best, but if you're interested then read on.

Flincher

Locks down enemy mons via flinching, making it significantly easier to set up a catch or survive a paradox fight. Functions perfectly fine without a passive, so you can assemble this mid-run and get full use out of it. If you do choose to run a passive, Skill Link ensures a 20-hit roll on Water Shuriken while Mold Breaker counters Water Absorb, Inner Focus, and Dazzling, the latter of which is notable for being Flutter Mane's passive. Running your own Dazzling nulls enemy priority moves against either of your mons, wasting their turns.

Water Shuriken is the flinching move of choice, as it's both multi-hit and priority. Extreme Speed lets you out-priority opposing priority users, assuming you're not running Dazzling to render them inert. If you are, it's still useful for Water Absorb mons. The last moveslot doesn't matter too much, but in the event that you somehow get into an important fight with one of your mission-critical team members down it's likely optimal to be running Revival Blessing here so your run doesn't end.

Example set:

Passive: Skill Link/Mold Breaker/Dazzling
Ability: Sturdy
Water Shuriken
Extreme Speed
Protect
Revival Blessing

Gale Wings Flincher

An alternative version of the Flincher, utilizing Gale Wings to convert Air Cutter into a spread priority move for flinching both enemies at once. You need the passive for this to work.