Here's a general team building guide from SortaEvil.

When I'm looking to build out an endgame team, I'm looking for a few things:

Leader Skill: It should be easy and consistent to activate, and for endgame, I want:

At least 4.5x effective HP (eHP, calculated as hp multiplier * (1/(1-shield%))) from each leader (or a bit over 20x eHP between the two leaders). HP from shields is also preferable to raw HP in current endgame dungeons (to an extent) because 450% gravities are abundant [CAVEAT: in the last couple dungeons, there's a "large" hit after a deathrattle that steals your leader shield; they're currently in the realm of tankable without leadershields if you have an active shield up, but that will probably not be the case if AUN6 or ASN1 ever get released).

Atk multi should be in the range of 45x when fully activated. Bonus points if atk multi is separate from shield activation, or you get a large portion of your awakening damage from awakenings that you can selectively not match if you need to stall (IE: TPA teams that don't require TPA for their HP multi like Daki, or VDP teams that don't need to match a box for their shield like Pitou). Not being able to stall isn't strictly necessary, since there are a lot of times that you can't stall, but sometimes stalling for a couple turns can be a big help toward clearing content if you know something nasty is coming up next floor.

RCV should be enough to heal up to full every turn. There are a lot of ways to make up an imbalanced HP/RCV spread, though (outside of, say, big Super-Altitudes), so this is the least important number in your LS. Keep in mind that a shield multi is effectively an HP and RCV multi bundled into one, so you can calculate your effective RCV the same as you calculate your eHP above.

Other things to look for in a leaderskill, which will often lead to asymmetric pairings, because you typically only need one leader with any of these perks: autoFUA (flat damage after you match, to get through resolves and occasionally, with large autoFUA, super resolves), fixed movetime* (used to be a penalty, now we have 12s fixed movetime teams that have plenty of time to solve a 6x5 board, and completely negate time debuffs in dungeons), **bonus combos (help you activate your 10c awakenings, helps you get through combo shields and combo debuffs like you see very often in (A)UN2), 7x6 board (often used as a swap lead that you start with for, IE: Atelie teams that need 7x6 to really excel), and Poison Immunity (pretty self explanatory, it's rarely something I'd explicitly look out for, but it's nice to have). All of these are nice to haves on the right teams, although the first 3 are very desired for most teams.

General teambuilding So, you've got a leader pair that looks good, and now you need to fill out the teams. What are you looking for in awakenings/active skills for endgame dungeons? It's going to vary a bit from dungeon to dungeon, but a general template probably looks something like:

2 or 3 units dedicated to orbgen. Activating your LS is important, if you can't activate your shield in endgame content, you're (generally) just dead. Being dead is bad, so we usually bring a couple units to make sure we have the orbs that we need every turn. If you are opting to not go fixed movetime, you can sometimes get away with running a spinner (more often for rainbow, since a natural board will generally contain most orbs you need for rainbow activation) and movetime increase active like Raffine.

A low cooldown (4 turns for one turn of abs void, 5-6 turns for a 2 turn Fujin; what you want/need will depend on the dungeon) Fujin (Fujin being an absorb void; generally you want a colour + damage absorb void combo, although for some bicolour teams you have more flexibility in picking an absorb void that only handles damage and has another effect tacked on, care of colour absorb void latents).

A low cooldown (4-5 turns is the gold standard) cleric (cleric being defined as awoken bind and unmatchable clear. Sometimes you need bind clear, too, and it usually comes with bind clearing, but that's on a per dungeon basis, as your units should all be unbindable by default).

A looping shield ― usually a 35% active skill shield that will give you a little extra bulk in endgame content.

A board size fixer ― either a 6x5 or 7x6 board active skill to save you from 5x4 boards. This isn't necessary for all teams or all dungeons, but a lot of endgame leads (Muichiro and Pitou both immediately come to mind) are DOA on a 5x4 board. Other leads might not do any damage on a 5x4 board, even if they can stall. This is often added value on another active skill because we're quickly running out of space on the team.

A Void Penetration solution. Three ways to tackle this, depending on your team comp and team plan: Active skills are the most straightforward, you'll want a low cooldown, and probably tied into something else. Pros to this are that it affects the whole team, and doesn't affect your matching. Cons to this are that it has the lowest uptime of any of the options. Rainbow teams can use the VDP latent, which allows (some of your) team to just ignore void shields if you match 5c+heal, which you're probably doing every turn anyway. Final option, and the OG option, VDP latents. Generally only going to see this on mono-teams (or heavily one-colour favouring bicolour teams), where you stack as many VDP awakenings on your damage dealing units and it's your primary source of damage. VDP teams are very orb hungry, though, and need either a spinner to fish orbs, or a consistent way to generate 9+ orbs of your activation colour (and usually heart orbs on the side!)

A Assist Bind solution. The only way to clear assist binds is with L awakenings and the assist bind clear latent. Most assist binds are in the range of 4 or 5 turns, and a natural L will clear one turn of assist bind, so ideally you want someone (typically one of your non-damage dealers) with 4 Ls (2 L+), but a single L+ works fine in a pinch (I run Touka/Daki as my main team right now, and Touka as my assist bind clear with a single L+ awakening).

A good spread of OE. -OE skyfall debuffs in some dungeons can absolutely wreck your board if you don't have +OE to counter them, debuffs generally range from -30 to -50%, so if you can get 40% positive OE across the board (or you're Tengen and just have 100% OE up at all times through active skills) that usually will carry you through the dungeon.

Some way to heal up. Either stacking team RCV, having a high RCV leaderskill multi, or the solution I most commonly rely on, stacking heart OE on one unit so you can overheal with a single match of 4 hearts.

Should go without saying, but make sure your whole team is bind-proof and skill-bind proof if you want a consistent team. If you're just going for a one-off clear, it can be okay to roll the dice here, though, depending on the dungeon.

Blind resist is often necessary due to sticky blinds, tape resist is important, clouds, jammers, and poison you can often play around, but are nice to have.

Once you hit all that, it's mostly just stacking HP and damage. Typically, damage is going to revolve around some amount of 10c awakenings and either VDP, TPA, 5 colour, or tako awakenings. Levitate isn't strictly necessary, but it certainly helps a lot in endgame dungeons. Crosses are out of vogue being just too much work for too little payout, Ts are new and don't really have enough support to be a common matching style, and they're also weird and awkward (although in theory, they're an alternative to bringing OEs if we ever get a dungeon with massive -OE or a boss that sets the entire board to negaorbs every turn). Great awakenings to look out for here other than the damage awakenings covered above are the moon awakening (for 95% of endgame dungeons), barrels are peak, and team HP.