Hello dear reader!
Since you are browsing this guide it must mean 2 things:
#1 - you play this forgotten, very nische and basically no-community game in order to get those sweet achievements while being stuck
#2 - you don't want to bother with editing files / want to do this fully legit way

If those are the cases, I'll describe step-by-step how I managed to finish the game in my playtime (should be around 3.5 hours ) without any guides (hence the reason for my inputs for that) and by scrabbing whatever I could. I personally hate that only way is not-legitimate, so I'll present step by step how to manage everything that walked / will walk your path

If it's not the case, then I'll hope you will grab yourself a drink and enjoy my thoughts and tips for this bad boy. And oh, man, it'll be some tricky stuff

SETUP:
What I played this game was straight up Veteran (3-star difficulty) Iron Man challenge, that I'll largely cover later on, on WINDOWED mode. You may ask yourself why windowed mode is important? For me, as I am not an osu player (at least at the time of writing) it helped in navigation for skills, which some of them I never trully learned nor I did them. To be exact, I assume fullscreen mode makes this harder, but I didn't bother to confirm that, so I may be wrong here.

What are our heroes and what are they exactly doing:
#1 - Main Guy with Gunsword - Personally I consider him the strongest from 2 reasons:
Reason nr. 1 - He has most versatile moveset as well as can hit both melee & ranged. Keep him alive for all cost as he can greatly manouver between enemies for faster wave clear.

Reason nr. 2 - He has (imo, but I highly doubt I am wrong) the best weapon on final stage, that grants lifesteal. When I aquired that he managed to save my run 3 times by soloing a stage ( more about solo in Ironman Challenge)

#2 - Lady Archer - She mostly fills out a support / utility role with healing, shielding and some Ranged-only damage. I used her for 80% of a run as a full utility character with going for more damage for the end-game. She may have potential, but I'd invest into main guy or

#3 - Hammer user - Very big DPS, especially with Strength gadget. He can with ease dishout around ~ 1k dmg for a single target across his 3 turns without high-damage weapon. What he lacks is in-general speed and ranged coverage, that in my opinion is relatively big downside.

Shop changes by the end of each chapter, so I'd recommend saving some gold for instant upgrades when respectively levels: 5, 9 and 13 are reached.

Chapter 1 is basically an early game, nothing really serious as I recall
Chapter 2 introduces poisoning enemies, so beware of that mechanic and grab some healing stuff
Chapter 3 has a lot of debuffs there, blinding can be detrimential
Chapter 4 is just a dps check

Story goes in this order:

#1 - Damsel in distress

That's the achievement for opening the game. Not really much to add about it

#2 - Sock Muppet

I recommend remembering soldiers moveset ( it was relatively easy ) since they will come back in regular timestamps for this one

#3 - Beard of Prey

Aquired when meeting up with 3rd party member


#4 - Hydra Down

Aquired when defeating first boss of the game


#5 - Party Crasher

If I am not mistaken, it's the last fight (really funny, but also not really easy) of 2nd chapter

#6 - Man Flu

Rematch with soldier squads, basically the same fight

#7 - Don't Drink This

Aquired with victory over 2nd chapter boss


#8 - Sword of Shame

Rematch #3, this time in 3rd chapter


#9 - Snake Charmer

This one you can get by finishing 3rd chapter


#10 - Cry me a River

Rematch #4, this time the last one, as you are in last, 4th chapter of a story

#11 - A Royal PTL

This one you can get by taking down last chapter, not sure after 2nd ord 3rd fight, by the end it should unlock.

Speaking of unlocking, if you defeated this chapter on normal / veteran difficulty you should also get:

#11.5 - Legitimate Success

Going by description, since last chapter has only 1 fight, higher difficulty should be required.

I also got it at the end of the game, which by the way is:

#12 - Quest Completed

Nothing here to add from my part, except citating a famous quote "Oh ♥♥♥♥, here they go again". Luckily ( or unfortunately) it's not covered in this game, so fear not, that is trully the end

So to begin with, what may be misleading is the fact that party is prohibited from using any items for all waves. In order to get those 4 achievements, you should be fighting with pure heart and skills only. You can always come back to the boss later / after Ironman challenge, so I recommend coming back for them later.
Those are, respectively:

#13 - Pure Hydra for Chapter 1


It was relatively easy, I 1st tried that on veteran attempt

#14 - Pure Beast for Chapter 2


I chickened out on 1st try because of poison, probably also doable on 1st attempt, after beating the game it was basically just a formality

#15 - Pure Serpent for Chapter 3


Here I was looking out about item ruling in previous fights, so I took it down after completing the game

#16 - Pure Boss for Final fight


What I did was going for fully maxed out 1st skills on all of characters and doing just that. If you struggle, I recommend this strategy

By doing that on Veteran difficulty you can unlock all 3 in one go, dunno if it's not mistyped tho. I don't recall that being any difficult and I didn't really notice when I unlocked that. What I recommend is to just get familiar with basic attacks and first skill and going all out on this one. Don't spice this out unnecessary, play it cool and it should be a matter of time.
Those are:

#17 - Epic for Begginers


#18 - Epic for Advancement


#19 - Epic for the Epic

So to begin with, in order that you should save yourself some time, go straight up for Ironman for Veteran difficulty as it unlocks previous ones.

About the strat: As I mentioned in Hero section, lifesteal weapon on main character should save you from any normal encounter, as you can solo everything up.
To clear a chapter only 1 character needs to be alive, so I sacrifice other 2 if you need to in order to win a fight - there are no downsides for failed comrades.
If situation is very stable - A lot of health on characters, spend time with other heroes for resting and restoring MP between waves. You can also cheese out some heals in between
Boss strat for me was spamming first ability on each character with last boss healing everyone with Archer. First part of those skill I think dictates overall damage, so you should get very good at it
If situation is very dire you can "reset" fight by going full hammermode ALT + F4 (tested that out and works). It will reset the fight with how you got there, but doesn't reset Ironman as it doesn't register as a restarting a chapter.

After this struggle you get:
#20 - Iron Man,


#21 - Legit Iron Man,


#22 - Ultimate Iron Man,


And to top this out, a freebie in form of:

#23 - Rock Star


That's All folks.

Well, that's how I did it. I hope this will help you, dear reader, if you are ever in time of need. I don't promise to respond any questions in comments section, but you're welcome to try. I highly doubt many of players finished this title up legit way (going by % per achievement numbers), I even truly highly doubt any players would read that, but you should know that I respect your dedication and wish you luck, not only here but in other games / challenge runs / nuzlocks / hardcore gaming sessions you are going to experience.

Have a good one!