There can be only one Hunter-Highlander.

If you have burned your chair in attempt to beat the game with level 1 sword, or in my case, with both level 1 armor and sword, this guide would give you a list of tips and the moral boost in order to push you to the limit.
P.S. I apologize for potential grammatical mistakes and lack of syntax/vocabulary. English isn't my 1st language so feel free to write comments if I made a mistake and or you need additional info... for some reason.

The challenge.

The difference between lev 3 and lev 1 swords is simple: lev 3 sword hits x2 faster and x2 harder.
Though majority of the bosses are predictable and not extremely annoying, some of them have very high dps and their stages' progression will lower your chances to kill them in time.
And, in my case, if you decided to beat the game with both lev 1 armor and sword, you will be in a nearly Dark Souls situation once you meet late game bosses: you hit 2 times slower and weaker than you should, while bosses deliver 1.5-2 times more damage on you.
The good news is that such challenge would prepare you for veteran mode and will give you, so far, deepest insight when it comes to bosses' mechanics.

Orbs and throwing weapons.

Up until Gael's Castle, these 4 aspects are your main focus and the only things that matters.

Soul Orbs
Orbs, duh, allow you to buy expendable weapons, heals and amulets.
Warning: DO NOT BUY ANY RESURRECTION AMULETS, until the final boss and DO NOT PICK UP THE FREE AMULETS DURING LEVELS' EXPLORATION. Just remember where they are and pick them up once you opened the portal to Priscus.

Axes.
The lowest damage and their ability to bounce makes a small remedy, yet they have feature: they fly on a straight line, which makes them the only long range weapon. Use this range advantage to deliver some damage before closing the distance with the enemy or going away from the enemy.

Torch.
Flames is the only proper "AoE" weapon you have. Unfortunately you can't use it under the water, duh, and some enemies are immune to fire, BUT, if used properly, torch can deliver 2-3 times more damage than axe and 1.5 damage of the spear. The short distance makes it useless against most of the bosses.

Spears.
Finally, the javelin, the only throwing weapon with damage equal to lev 3 sword and it has the most absurd trajectory. You should practice throwing this weapon on aqueduct level (10 free spears), so you could use it instinctively on late game bosses. Javelins are essential for your hindquarters survival, since it will be the only damage dealing weapon at your disposal.

Late game bosses

They differ little to early-mid game bosses. There were only two major problems before the Gael's Castle stage: Man-Eater and Leviathan.

Aside of fire immunity, Man-Eater has absolutely no defence against your attacks but you can only hurt him by hitting his girl-tongue (reminds me of Sponge Bob ice-cream monster on their way to Shell City)
Attack him with your sword/axes and maybe with spears, but once the tongue girl appears, go to the left corner and hit the tongue with 2 spears. It took me 8 spears to finish it in total +-24 spears for the Man-Eater (it is hard to miss the Man-Eater itself and unacceptable to miss its tongue).

Leviathan is somewhat the opposite. This fish has lower dps, but higher defence, since you cannot penetrate its shell, while attacking the heart.
Predict from which side the Leviathan would appear, go the opposite and throw as many axes as possible. If the fish moves slow, you can try javelin, if it's fast, use axes and sword. The larvae attack is the most dangerous and either you sacrifice some health to kill them all, or use spears to finish them... which is hard due to intense fight.

In time you will be able to knockout every single boss and you will enter the Gael Castle. You will be somewhat pleased with the amount of orbs from knights and Shao Kahns, then you will meet Albey (in my opinion, the weakest late game boss) and eventually defeat her and then... then comes your biggest challenge and the hardest boss in the game - Amargein.

That wannabe Nazgul is the most annoying and hardest boss to hit. It took me 5-6 hours, before I was able to remember his moves and it will take you at least 24-30 javelins (make sure you practice throwing them while jumping, flying, dashing).
Hitting him with 8-10 spears, before Blue avatar spawn is the most important + 3-4 sword hits.
After killing Blue avatar (without loosing any health of course) you must hit him with 6-7 spears + 3-4 sword hits, probably sacrificing some of your health.
Red and Yellow avatars are somewhat predictable, just stay cool and don't rush, throw axes and torches in them, but never dash to them to hit with the sword.
Funny or not, I killed 3 Yellow avatars before my final kick on that Lich. You of course, could do it with lev 3 armor, but even then, you must practice a lot with hitting Red and Yellow avatars in order to damage the real Amargein, without taking significant amount of damage.

Immanentize the E(s)chaton

The final boss would look like a joke, after Amargein's nightmare.
The 1st stage can be cleared with 24 axes (better not to risk your health even if you have lev 3 armor)
The 2nd stage can be cleared with 10-20 javelins + sword hits (throw the spears when Priscus is levitating and also avoid any hits from him during this stage, use sword only during his range attacks on a ground)
The 3rd stage was considered quite disappointing by some players because the only good thing about Odallus' true form is the design (Lorgar would have been pleased).
In your case however this stage would be way more challenging. The gem has somewhat 30 hp, which equals to 15 javelins, 20-30 torches, 30 axes and 30 sword swings. You can hit the gem 1-2 times per boss attack and some of them could take you by surprise even after some practice (fails), yet you can always throw any weapon at it and hope for a lucky hit, which is actually a good way to kill final boss. Stay as cool as you were during Amargein's fight and in time you will knockout that Daemon Prince.
And yes, this is the reason why you shouldn't have taken/buy any resurrection amulets. Go to the previous locations, take all free amulets and practice the boss fight. Once you have some experience with Priscus, farm 1k of orbs on kingts/Shao Kahns in the Gael's Castle, buy everything in the shop and do your best.
Warning: THE SHOP ON FINAL STAGE IS BUGGED, BE CAREFUL WHEN USING IT AFTER DYING DURING BOSS FIGHT. Maybe it's just me, but when I used it after dying, the game crushed every single time.

Epilogue.

If you find this guide useless and pointless, just go YT where you will find proper walkthrough and boss fight mechanics (though there are no highlander videos... which is the reason why I decided to write this guide).
It's a shame that I didn't discover JoyMasher's games before buying and completely beating Blazing Chrome. I am looking for the Moonrider, since this game would be an improvement over all Danilo's previous games and I hope it would be great.
Again, if I made any mistakes or missed key elements/info please correct me.