OK, so first off...
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The preparation:

I'd recommend at least 5,500 Units. You can have 2,000 Units worth of Revives and 3,500 Units total, just make sure it adds to the amount I stated. You can get away with 5,000 but you want that security.

The toughest fights for me were Civil War Black Panther, Netflix Daredevil*, Venompool and Maestro. But Doctor Strange's specials are no joke. Use your duels and practice against these guys and I'd recommend taking the middle path in Act 4 Chapter 4 Quest 6 and practice that L1 from Maestro (don't worry about DD, I'll get to that).

Make sure you have a good amount of attack boosts (the attack and health boosts are good too) and potions (pots are huge for parrying and against DS, because you'll have to take special attack damage). Also, try and check out the Loyalty store and look for the class boosts for Tech. You want that 8% attack boost for some fights to your specials for S-L. 150% increase of Power Gain is good too.
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Entering the Labyrinth:

I'd recommend a team of Wolverine, Magneto, Storm and Cyclops. Those critical hits are amazing.

Time for actual fighting. You want to get a good start against Red Hulk. Try and get 500k off first try, if you can't, I'd say exit and keep trying until you do. Activate some boosts after that. You want to blow through Red Hulk, Old Man Logan, Elektra (wouldn't hurt practicing that L1 also), Ms. Marvel and Unstoppable Colossus.

Watch for that Gold Symbioid, he's not that big of a deal but he has Juggernaut's specials.
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Enduring:

Now you're gonna be hitting CWBP. No parries. And his buffs make it a long fight considering the 2.1 mil health. Makes it deceiving. But keep at it and make sure you have attack boosts and the Tech boosts activated.

*Here's where that star comes in... Netflix DD looks like a pretty easy kill right? Yeah, thought so too. He might've been an easy kill for some but he evaded so much, it's not funny. Play it fast but smart. He'll inflict a degenerative debuff on you if you hold your block for too long.

Venompool up next. Probably the toughest fight behind Maestro. Such a bastard. He doesn't use his specials as often as the others and he'll back you in the corner a lot. Be ready to evade those heavies and he's gonna try and bait you with the L2. Watch for it. I'd recommend heavy boosting for this (attack, attack/health and Tech). It's a very ugly fight...

Now, it's basically second nature to try to evade specials. I recommend taking the special damage from DS. Not all of it, just the initial damage. With his special 1, take that first hit, evade the spell. 2nd special is not worth the risk, take the two hits, evade the last one. Be patient. I'd recommend 20% attack/health boost, Tech boost and healing up to 75%. Attack and Tech boost for his armour and health and pots because of the blocked damage. (Side note: This didn't happen to me but when I watched Seatin fight him, he got hit by his L2 while he was in his Power Gain buff and regenerated quite a bit. Force quit immediately if you happen to get hit by it and he's in his Power Gain buff).
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Finishing this damn thing:

Kamala isn't tough but you can't Parry. Play smart. Use a 15% attack boost because of the class disadvantage. If you don't have one, a 10% attack/health will be fine.

Rocket. Just kick that trash panda's ass, lol. And don't push him to his L2.

Now, the grand finale to this God forsaken maze, lol.
Maestro. OK, he will start with one really shitty buff (one is just a slap in the face). It can be Power Gain, Unstoppable or Regeneration (the slap). Force quit on the regen unless it's the very first fight you do (wouldn't put it past Kabam doing that). He'll gain one more during the fight. Power Gain, push him just to his L2 and start baiting like your life depends on hit. Try to control it best as possible while still getting good hits in. Play it smart but don't be too passive. (He can stack Power Gain BTW...) Unstoppable isn't too bad. Use your parries and evade. Mainly parry though. You don't want to get cornered or caught. Regeneration... F#$&ing money grab....... Just force quit. The L1. It's tough to get the timing down because of how long ago Act 4 was finished. Like I said earlier, it would be best to practice on him with the middle path. Or watch videos. If you get it down, you're gonna be in a whole lot better of a situation. Boost up with all the attack boosts and Tech boosts, it's the final fight. And heal up to 55-60% health. You're gonna take more damage than the previous fights when you Parry and you're gonna want to Parry him more often than usual. Good luck with him and pray he regenerates as few times as possible.
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Tips:

It's gonna be a bit more fast-paced compared to fights outside of the Labyrinth. Play it at a pace that you feel comfortable with, when you can.

The evade... Oh man, the evade... It's such a damn piss off and it's always in the back of your head but you gotta try not to think about it. Once you really hit that groove and you lock in, you're gonna forget about it but the amount of times it evaded my L2... So saddening :(
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So that's my guide. If you have any other questions, let me know. Good luck and kick ass my friends!