I feel like if you can reach the fight in reasonable condition, you're favored to win. Sustain and scaling matter a lot, as usual. Got there for my first time recently with a relatively bad set of gems (2x Lv 3 multi-target damage, 2x Lv3 Shock, 2x Lv3 Shield+Thorns, 2x Lv2 single-target Heal), but had three maxed Silver units to make up for it.

There's no need to rush past the initial boss phase. If you're strong enough to handle what's after, then you're strong enough to top off most to all of your HP before the initial phase ends, especially if you have access to higher quality/level gem heals than what I did.

The second phase for me was about getting some Shock down fast while the boss is warming up (one or fewer skill procs), then spamming Shield the rest of the fight. If you have one or two characters who are particularly tankier than the rest, its probably possible to attrition it down with passive damage like Burn while your tanks heal stall.

I only had one single-target healer plus one self-healer in my party, so don't feel like you have to force any of the Bronze healers. Unless your Traveling Merchant options and general luck were both terrible, you can get by without them.

The best silver healers seem to be Selen and P.I. Petri. They have strong heals plus give illusion and barrier respectively. If you have Chrome and Bron as your tanks, they'll basically never go down with a decent build of symbols.

If you want an actual specific strategy, try to unlock those units and build towards them.

if you made it past ancient lab you likely already know this, but i'm going to state it again because it's important: once you have unlocked a hero's symbols by getting them to tier 2/silver star, you can sell them and still keep the symbols. i had 15 symbols when i first cleared witch's maze.

magic hammers give you 10% of your gold and have 2-4 uses depending on tier. there is also a random encounter where you can throw your gold into a hole and receive double your gold back a few floors later. to extract the most value out of these, you want to conserve gold - i decided early on that i would not bother trying to get any hero to t3 and held off on buying the last hero slots until i really needed them. it is perfectly fine to just barely scrape by the early/mid game and invest for late game.

the same goes for crystals. gems always cost 20 crystals, but later in the game you can buy t3 gems for the same price (still, if you need to buy a potion or mana go for it, crystals are plentiful). a lot of people say shield gems are good, but i had much better luck with t3 rainbow blades (60 damage 7 times, 6 turn cooldown) so i went with 5 rainbow blades + 2 shields and it actually worked pretty well. rainbow blades do respectable damage with sunlight t2 but it also triggers shock damage seven times, it ended up doing more damage than my team.

if you can get thief earrings early game they'll make something like 300 gold for you over the course of the game, they're worth keeping even without the best symbols.

otherwise for earrings and rings, pretty much anything is fine as long as it has valuable symbols. which symbols are best for you depends on what heroes you have unlocked, in my case i favored green, sunlight, and shield since i needed help getting those symbols to t2. for necklace, you ideally want either of the defence command necklaces but getting good symbols is still important.

healers are pretty bunk for the final battle since the only way to scale up healer skills is to get the hero to t3. i had spessar the bard but i think i would've been fine with no healer at all.

this isn't terribly obvious unless you look at the final boss' skills, but her physical skill only hits one person on your front row (and generally targets the first hero) and her magic skill hits 3 people at random. both skills hit multiple times so any sort of flat damage reduction is extremely effective here.

you should still expect your first tank to die but the battle should be over before your second tank is even at risk. king's shield bron is likely the best tank, but green wind chrome is good too. stalward knight dia has pretty good physical defence so she's not terrible at sitting in the front.

you should not need a lot of things unlocked to finish the witch's maze. i did it at around 20 unlocks... i think if you have the free mana potion, enough blue/green/shield heroes to hit tier 2 of those symbols, and heroes who can inflict shock (they don't need to be yellow, the yellow symbol kinda sucks for boss fights) you should be fine. you probably also want sunlight t2 to be doable if you're going to try rainbow swords like i did.

if you really want every advantage you can get, the game gives you one piece of jewelry at the start of the run if your last run was a success, i'd assume you can just run an easy dungeon before attempting the witch's maze to get some free jewelry.