First you want to max out Brutality, which gives you the currency you are spending in the shop.
To make this easier, you should also develop Magnet and Lucky Coin.
Just with these, so no actual progress in the game you will be able to beat the first two area, and even Master them. But The Roof is a hugh wall, so back to grinding.

You probably started to invest into Greed, what makes you level up faster. You do NOT gain exp by defeating the enemies, oh no. You have to pick up the money they throw, that counts as exp. No, you don't pay with money, where would that lead, right? (You also gain more money from Lucky Coin.)
Then there is ReRoll. Given the nature of this game you should get the extra rolls EVERY TIME YOU LEVEL UP, but someone again not thought things through, so there goes your funky combos. Either way, this again won't make you stronger, but you'll have to build it up ASAP, so you can actualy focus on this.

At this point you grinded probably for like 2 hours, and fed up with the first two area, but never mind that, get back to grinding! Because the next area is The Roof, and let me tell you, it sucks. Give up your hopes on relying on manouvering around and using the environment. You'll run out of those like at the third of the necessary runtime.
So what to do? Well, you'll need at least 2 point in Speed, max out Agility and Thoughness, AND pump up your own strength.
To not just grind for money and run away in boredom, let's take a look at the unlockables. They either unlock cards (which you already have too many to pick from), and use of the environment, also some extra spawning items. So don't expect to find a Burrito soon for example. Nor Ninja-stars.

For me getting all Bleeding-perk was the easiest. For some reason those cards are aplenty, and you mostly just have to deal damage with it, so it unlocks naturaly if you pick those cards. The "defeat boss X" can't be helped, and targeting knife-ladies is a hassle - pick them when you are grinding though, just to spend the time.
Also do not expect to find anyone with a loudspeaker. Dunno when they show up, but seems not at all in the first three area.
Completing all level on Master diff is also out of the question as first you have to unlock them (for some reason you can instantly try Master diff on any unlocked stage, but Legend only seem to unlock after the 5th area is mastered or something).
So the next I picked is Piercing damage. For some reason picking off enemies with this rarely happens, so "good that we are grinding anyway", hah. If my suspicion if correct, after the "kill X enemies by piercing" all the rest will instantly unlock, I'll report that.
There's also a chain of Knockback damage unlockables, but I think on the cards this is actualy "Push" and not unlock, and another thing is, I have no idea what a "miniboss" is, so I neglected this branch. The attribute is the rarest anyway from bleeding/piercing/push.

Also don't forget upping ASAP your regenration rate.

What Luck does is not just effecting your possible card-pool and how large bonus will be on the stat-boosting cards, but also the chance to spawn chineese food package (whatever the actual name). It gives you a large amount of HP. No, it is not fully healing you - this you can notice if you picked up a bunch of +X Max HP card.

The "kill enemies with a bat" (knockback chain of unlockables) means the enemy should have the bat, meaning you can only unlock this tier if you are on at least The Rooftop.

Oh, and as we are tlaking about grinding: grab additional Gun and Shotgun shots too, as that's an unlockable, and for a looong while those will be your only "super weapons", and you need to pick off 5,000 enemies with them. I'm still stuck in the first 2 area, 1 more go and will unlock probably everything that is possible for now, and I'm stuck at 3,000 without upgrading these perks.

There is this unlock which says you have to consume energhy drink and burrite "two times on the same level". We already mentioned you have to unlock Burrito first, but then also is the fact these things do NOT respawn. So you have to play a level twice. That's the way it is.

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Started Rooftop with not maxed out Control, Life and Chi, plus zero point in Throw, Movement, Monumental, Sharpness, Knockback, Combat. Shuriken is still locked, 3,500 victims out of 5,000.
It was easy. The trick is do not move, and let your character build up with 3+ moves, range and strength mostly, so you can eliminate entire armies as a dervish of destruction. Yeah, balance is out of the window with my progress it seems. And I'll have to do Rooftop twice more, as I only found 3 girl with bat (and complete baseball-gear) for some reason, and now I need to pick off 6 for the next unlock. At least I do not have to ocncentrate on Piercing anymore, though that definitely is convenient as crowd-control. Also: at this point I have 4K people offed for Shuriken. Yes, I'm paying attention to the unlocks. They make life easier, at least supposed to.

When beating the Subway Boss I still had 500 kill left till Shuriken will be unlocked, and still have to do some Knockback damage on bosses. If I get "Push"-cards, that's not that much of a problem I think, Subway-boss has a ton of HP, and with adequate developing each hit can deal like 1,500 dmg. Still, I thought should be mentioned.

Ok, so now I did all the Master Diff. Still have unlocked:
- Shuriken (33 kill missing)
- 20K "knockback damage" delt to boss (seems cumulative if you care. Also, Knockback does not do damage, this means the strikes - punches and kicks - which do "Push" must deal that amount of damage)
- there's finaly this weird line of skills in the middle (3rd from top and bottom too) bracket which starts with the Sickle-unlockable. My next will be Axe.
For Upgrades I have only:
- 3 stars in Life
- 0 in Monumental Master
- and finaly Burrito is still locked.
I mean this was before I spent my teeth from the last run, so now maxed Life and have 3 stars in Monument.

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There is a bug, where the fact you've beaten the Construction Site Boss (Area 4) is forgotten by the game. To fix it, start any level and immediately quit,

Legendary Rooftop is totaly hard. You can get hurt too easily too fast, there's no space to move around, and you don't get loot fast enough to build yourself up. There is a 5% chance I see everything falling in place and my attention don't slip, but it looks dubious.
Subway I also hesitate to touch, as that also had the same problem of not gaining enough levels fast enough on the other difficulties. I'm not sure which'll prove harder.

For Legendary Construction Site I picked Luck over anything, and it was very-very hard until 10 minutes, where finaly I became pretty much invincible. Damage just have to hold up, but it's dodge and block what you actualy need, else you'll get toast. There are just too many enemies there. Also do not move around if you don't have to. this is another probelm for Rooftop: there's only 1 closed room, so Shuriken and food is very rare there.

Oh, before I forget: Styles. There are 3: red, blue and yellow.
Red is fast, but usualy don't have range/reach with its moves. But if you sequence the moves right, you'll get aura-effect on every move, which can reach from half the screen to the whole screen, so it can be devastating.
Blue is a good middle-path with kicks that have a wild angle and good power right from the getgo, and build up a nice penetrating directional shockwave for crowd-control.
Yellow has the highest starting damage, and can go in weird angles with its moves. The worst part is it either has no combined effect, or just some tiny fireball a'la Kung Lao in the original Mortal Kombat movie, so it's not that good.

Another tip though: if you can get like 2 "attack behind" move at the end of your sequence, then you can easily turn the direction your moves will effectt he enemy anyway. This method also makes running from the enemies easier, not to mention the actual bosses.

This reminds me the topic of minibosses. Well, they simply have wa ymore HP than a normal enemy. At least I did find a knife-thrower girl which turned out to be a miniboss. Minibosses leave behind a suitcase with the usual content (extra card/s). There is one unique miniboss though which I first met on the Subway, but "going back" doing Legendary 1st area it also shown up. It's a dmaage-sponge giant on which a dwarf is sitting. Kinda like that character in Mad Max 3. takes forever to kill, but is mostly not harmful fortunately.

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Well, it took me a while to figure out why I am dying on the roof even from max HP to 1 hit. "Minibosses". Those units with insane HP, and no other way to distinguish them from the rest (also throwing a suitcase when defeated).
Yes, they deal INSANE damage, so you have to build up your reperotoir, enough damage to oneshot even the "fat" enemies, enough range to eliminate entire mobs, AND get enough extra Max HP AND enough regeneration to be able to survive ONE accidental hit from a miniboss.
Also pump up luck in hope of food to drop.
AND do not move around AT ALL if possible, just find a rooftop with a one-screen kinda-open area with not tricks, and actively run aftert he enemy and the money. For that also pick up some magnet-upgrade, it does help somewhat.
Also asap use up ALL weapons lying around, they SUCK, they'd get in the way otherwise.
For the greenhair lumberjack/wall: preferably don't bother getting close to them, that usualy means luring enemies from another rooftop too. On the other hand if you can cut a hole into them just in case.
Lastly keep in mind if you get in a desperate condition, the NW corner is the Closed Room with food, and if you unlocked it, shuriken. Also a suitcase. DO NOT pick these up unless you progressed far and/or you are in a desperate situation!
Oh, your very last tool in the box is the Whatever Lotus card, which even on Legendary diff makes you totaly immun,while makes you eliminate any enemy you touch!
So this area IS possible, the biggest burden are the "Minibosses". Be paranoid for them!

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For Subway Legend you need a couple of real life luck things to fall in place.
1) you need the same colour attack-row
2) they must have high damage from the start (definitely aim for 150+, more like 400+)
3) they must be a chain (numbers following each other, eg. 10, 11, 12, 13, 14). You can miss 1, maybe 2 an use something like "Axe", but generaly true.
4) they all must use reliable direction and wild angle. So Yeloow Cards are mostly out! Most likely you'll use Blue Cards, as this level don't like to give you red cards (or they'll have very low damage. like 50, and that's simply not enough).

Also skip Luck cards until you are definitely set up, because they are rare and do not drop enough "loot" (magnet, and over all: food). Focus on raw power: damage, range, ca. +10% walking speed, +100 pickup (eventualy you'll have no better choice anway, and 1-2 of +75-100% card does help), and leveling your cards. USUALY leveling your cards this time IS NOT the outmost preferance, but pure damage! That buffs all your cards, and you rely on raw power this time to survive, meaning you have to build yourself up to actualy kill the hordes, no joke!

For positioning I found staying at the bottom of the map on that long corridor is what you should do. If you are forced to go the upper horizontal corridor, you'll get toasted by dynamite-throwing enemies and such. So stick to the upper side of the southern horizontal corridor, and go left-right as needed. While tempting, avoid getting stuck to the bottom (southern) side of this corridor, you'll be mobbed for lack of positioning! For the constant movement you need to use space between enemies, that's why you'll need some extra speed (minimum +8%).

There are also minibosses, but they usualy won't be a problem. But if you spot one, definitely keep distance from them, THEY HURT.
Eventualy you'll have the chance (for lack of better option) to buff your block/dodge, but this is an illusion, always buff your damage first! that's how you survive this level, and become Legend.