In total there are currently 8 different characters. At the start of the game you will have 5 of them aviable: Kirie, Aiko, Haru, Mizuki and Kouji. Every one of them has different stats and character-specific percs which can be accessed by a Level-up. Each Level-Up will grant you acces to 1 out of 3 percs and 1 Skill-Point OR the option to heal Reason or Stamina by 3/4/5 depending on the difficulty.

I would highly recommand to chose 1 "Main-Stat" either Strengh, Dexterity, Knowledge or Perception. Most of the time you want to use your skill-points to increase the highest stat.
Kirie -> Knowledge
Aiko -> Dexterity or Strength
Haru -> Strength
Mizuki -> Dexterity (or Perception)
Kouji -> Strength (or Knowledge or Perception)
Mimi (unlock by beating the game twice) -> Knowledge
Miku (unlock by solving the Rioter-Puzzle) -> Strengh (or any other stat)
Moriko (unlock by solving the Lost Girl-Puzzle) -> Perception

Remember that the "basic-percs" will increase a stat by 1 aswell. Chose a weapon which fits the selected stat. I will explain the weapons later on (strategy and how/when to get them). Rise the selected stat until it reaches a value of 10.

Do not waste your valuable skill-points on healing, unless you are below 7 Sta/Rea and are about to face a tough enemy soon OR your Doom is to high to risk the rest-option. Use the rest-option and baths to heal, forget a spell or even buy meds, when your town suffers under the "contaminated water" or the "Smog"-Status (Experimental Drug and Pain Medication cost 3 Funds, but heal by 4).

But why should you chose a Main-Stat? A lot of your strategic decisions will be determined by the Stat. This guide will give you plenty of advices and tipps to perform and prepare for combat.

Weapons have 1 out of 4 categories (Strengh, Dexterity, Knowledge, Perception) and 3 values: Damage, Accurecy and Speed. By maxing out the stat, which fits to the category of your weapon, you will influence the Accurecy and Speed of your attack-actions during combat.

On the other hand, taking a random weapon will limit your battle options tremendously.

How do Stats interact with weapons and combat options?

Strength: The higher your Str is, the faster you can perform the "Block"-Action, which will cut the damage of Attacks classifed as "-X STA" or "-X All" by half. The values are rounded down, which means, that what would have dealt 3 Damage, will drain only 1 Damage after blocking. "-X REA" classifed attacks cannot be blocked.
Your Strengh has inpact on how fast your attacking-actions are, when wielding a Strengh-Based-Weapon, which are listed below.

Dexterity: The higher your Dex is, the faster you can perfom the "Dodge"-Action. The chances of a succesful dodge seem to be calculated through your Dex-Value and the enemies "Power"-stat, which I cannot confirm tho. I realized, that dodging is succesful frequently, when my Dex was high.
Your Dexterity has inpact on how fast your attacking-actions are, when you wield a Dexterity-Based Weapon, which are listed below.

Knowledge: I cannot yet confirm that the Knw-Stat has any influence on battle except making attacking-actions faster, while wielding a Knowledge-Based-Weapon.

Perception: I cannot yet confirm that the Per-Stat has any influence on battle except making attacking-actions faster, while wielding a Perception-Based-Weapon.

Charisma and Funds have no inpact on combat.
I don't think that the hidden Luck stat has any influence on combat, which I cannot confirm aswell.

At the start of each run, the first thing is to take a bath for 5 bonus exp, watch TV till you get the missing-girl-report and check your Mysteries. Depending on your main stat your strategy might differ. But here are some general, recommanded actions for every character and build:

3.1 Order of Mysteries and Boss-Enemies
Never do Myteries with Hard boss fights first. It is way better to gain Level 3 or even Level 4 and collect some items, spells, allies before facing these enemies. Having your Main-Stat at 10 and a fitting weapon will make these battles fairly easy:
- Aka Manto
- Scissor Lady
- Mad Janitor (skip by burning the school -> Burned Wounds - injury)
- Dream Devourer (skip by not doing the side quest -> -3 REA)
- Horrible old man (skip by killing all guests)
- Fungicide (skipable by not doing the side quest and ignoring Shiro-Sans Wounds)
You are either really good equipped and strategized well or an idiot if you attempt to face and kill multiple bosses in a single run. The following aspects will involve more tipps to chose an order in which you solve mysteries.
Generally you will need some experience to decide which fights you want to avoind and which you can face without throwing the run.

3.2 Allies
Most of the time, the first mystery should give you access to the towns menu. In the town you can buy a weapon, recruit students, lern spells and visit the witchs tree (unlockable location/usefull in hard mode). If you have access to the Evolving Eels-Mystery, do it first to get Kana to follow you. She will reduce all incoming DMG by 1! I also recommand doing the Far-Out-Festival-Mystery second, since you can recruit powerful allies in trade for some stats.
Examples:
-> Ryoko: Increases your DMG by 1!
-> Iwa: +2 Strengh!
Since you will investigate the forrest, you might even find the Dog-Ally.

Always visit the school and ask for the students to help you right at the start of the game. Do not "wait" since the doom costs may cost you the run. If you will face Aka Manto anyway, wait until you face him in the 3-5th mystery before recruiting allies. Always check the students percs, since they are randomized! Some give you a small stat boost, some give you percs, but some decrease a stat by one. You can let them go OR use them otherwise (for a mystery or in combat).

3.3 Spells
Visit the library and learn a spell or 2. Doing this is high risk (rise of Doom in exchange for nothing usefull) and high reward. Most Spells are useless, but there are some usefull ones:
- Flesh Regrowth -> Helps you to manage your Stamina
- Skin Removal -> Helps you to deal a finishing blow
- Regenaration -> Trades Reason for Stamina
- Memory Extract -> Trades Experience for Reason
- Ithotu Flame -> Deals 7 Damage for 3% Doom and 1 STA and REA each
- Expel Evil -> - 6% Doom (ceep it for the Lighthouse or use at the end of the last mystery if needed)

3.4 Items
Buy items: If you hit 0 Funds, the strange salesman will appear and provide you with 2 Funds in exchange for -3 STA, -3 REA or +5% DOOM. In my runs I look forward getting this encounter 2 times. What should you buy? Ofc a weapon is nice, unless there is a Fund-free way of obtaining one, which I will list below. Otherwise I recommand to buy one of these items on your first mystery (priority on the upper items):

- Flashlight: Provides +1 Perception and is a must have for the Perc-Build. It also gives you access to solve multiple events and mysteris! The Flashlight can be obtained in the Hardware-shop (and sometimes in the Dog-Shop)

- Holy Candle: If you have unlocked the "ocult-shop-location" or have access to the Far-Out-Festival-Mystery you can Buy this for 2 Funds. This item gives you 1 Luck and is necessary for 3 random events, in which you can use it without loosing the item. This will lower Doom and can be a absolute run-saver. And on top of that you can use it to heal 2 REA. This item is worth the Funds.

- Compass: If you visit the Dog-Shop you can obtain the compass. This will give you +2 Exp for every Event when equiped in the C-Slot. Buying this item early will grant you fast Level-ups. You can boost your Main-Stat fast and get percs to prepare for skill-checks and events.
If you get a weapon without spending funds you should probably get this item beside the flashlight. If you already have a camera or some other B-slot-Item (like a mask) and you can buy this item aswell. It is most usefull at the start of the game. You can sell it ones you reach Lvl. 4 to obtain 1 Fund ( or if you need 1 Fund)

- Camera: In the Dog-Shop -> +1 Knowledge, good for all Knowledge builds. Gives you the combat-option to lower the enemies "Power" (under support-actions) which boosts your accurucy. I think the Flashlight is a better B-Slot-Item. But for Knowledge a camara is ok.

- Ritual Puppet: This item can be bought in the occult shop for 2 Funds. It will deal 4-6 Damage at the cost of 1-2 Stamina. It is a item, not a weapon, which means that you can use it multiple times, even against the same enemy. I don't have to explain why this item is very useful.

- Map: Usefull for events where you have to check the forest (farout-festival and -freaky-footage-mystery). You may buy this if your doom is high and you have to do these mysteries... otherwise visiting the shop costs doom aswell and there is no guarantee that this item is aviable.. Consider buying it, if you miss the chance for a flashlight or compass.

On Normal difficulty, you will have 4 Funds. On Hard, you should have unlocked the "witchs-tree-location", to at least get 2 Funds for a weapon. Getting a weapon first is really important, but you won't have to buy one on every run. Below I will list the aviable weapons and approaches for each Main-Stat.

Strength:
If you have chosen strength as your Main-Stat, I recommand you to start the Violent Vigil-Mystery, since you will get access to the meat-cleaver weapon, which can be found in the storage room. It is a free weapon, with a damage-value of 4!
During the Evolving Eels and Abnormal Arms-Mystery you will have to investigate the Apartments area frequently. This will give you a 50% chance to encounter the Apartment Stalker, which often drops his Baseball-Bat, one of the best Str. weapon in the game.
These 3 Mysteries are the best to start with, when you chose STR as your Main-Stat.
The Wooden Bat, which can be found in the school lockers during the School-Scisors-Mystery, is a different item and not quite as good as the Baseball Bat, but still an viable option. You will have to fight the Scisor Lady early tho.
You can visit the Hardware-Shop on the seaside and purchase a Strength weapon:
Carpenter Hammer: Its only 2 Funds and my weapon of choice, since I can buy one more item with my remaining 2 Funds. Its a fast weapon, but will require the "prepare"-action during combat, since its accurecy is aweful. Still I think this is the best option, because of the costs.
Shovel: High damage, but really slow. I do not recommand this weapon.
Crowbar: It gives you an additional option during the fight against mad Janitor. If you have a lot of funds you can get this instead of the Carpenter Hammer, since it provides a lot more accurecy.
Ofc you can just search for a weapon during combat and find a branch. It is a slow weapon with little damage, but better than nothing I guess. If another weapon is aviable, I would rather run from the fight.
Another option is the Flamethrower Weapon. This Weapon is only aviable by doing the "Lost-Botanist-Mystery". If you want to know exactly how to obtain the Flamethrower, here comes the spoiler:
The Flamethrower won't be your weapon to start with. You will need to accomplish Ending A on the Botanist-Mystery. In order to do so, you will need to kill the Mad Janitor (Mermaid-Mystery) by combat and loot his Fire Ace. Enter the Lab in the Forest with the Fire Ace equipped and choose the combat action "cut your way through" (or something like that). You will then recieve the Flamethrower. I haven't tried this weapon yet, but will play the game again on the next patch.

Dexterity:
If you have chosen dexterity as your Main-Stat, good luck finding a weapon, since you'll need some luck. In the Dog-Shop you can buy a steak knife. Another option is the Young-Witch-Encounter. Defeating her will provide you with a steak knife, which surprisingly happens to be one of the most powerfull weapons. With maxed dexterity you can dish out 4-5 light attacks in a single turn to deal up to 30 damage per turn (20 with Ryoko-allie or ancestral Strength, 25 with both). The old God Ithotu will increase your DMG aswell (= Maximum of 30 Damage with 10 Dexterity and all possible bonuses). You might prefer the steak knife with its fast speed over a strength based weapon, if you have that God selected.
You also have the option to search for a inprovised weapon during combat. There is a high chance of obtaining the broken bottle item, which isn't that bad actually.
Another rather rare item is the katana. It can be found in the Otherworld, by either using the Void spell or encountering one of these events: Iillusion Shattered (village or forest, enter the portal) - Half Open (school, enter the door) - Tower Window (mension, fail strengh check or get lost in the light) - There is one more a event at seaside (I think?), I don't know the name of..
Entering the Other World will teleport you to either encounter the boreal expense or the bleeding desert (50/50 chance?). In one of those you have a small chance to obtain the katana. I had no chance to try that weapon yet.
If you want to know exactly how to obtain the katana, here comes the spoiler.
In the Bleeding Desert you will get the option to explore the temple, where you will find the Katana. It requieres a really high roll on a strengh check and will cost you -3 Stamina, if you fail. In Otherworld Locations you have -3 on all skillchecks. This makes it really difficult to obtain the katana, making it pure luck. I have't tried this weapon yet, thus I cannot say if it's worth the risk.

Dexterity is a great secondary stat, since it reduces the cost and increases the chance of the dodge-action. If you have high Dex and find a steak knife, you might even consider maxing out your Dex in middle of your run.

Knowledge:
Currently there are 5 Knowledge-based Weapons. The Scalpel and the Bone-Saw can be found in the Pharmacy (Hospital). You might want to recruit students first and hope for the "Cost of Pharmacy-Items reduced by 1"-perk. The "Ritual Dagger" can be bought in the "occult shop" or obtained by the event Seaside Ritual. The best Knowledge weapon are the Cursed Scisors.
Scalpel: This item can be bought in the Pharmacy (Hospital) for 3 Funds. It is a decent weapon, with some investment in Dex or Str it can carry you through the game.
Bone-Saw: This item can be bought in the Pharmacy (Hospital) for 2 Funds. It is a bit slower than the scalpel, but has higher DMG and deals Bonus damage against few enemies (undead which were intruduced in the botanik-update)
Samll Candle: Can be optained in the occult shop for 2 Funds. It is a good weapon. With 10 KNW (Buy a camara on the start) you can deal 15 DMG in a single turn. With 10 KNW it has 80-100 Accurecy, depending on the enemy. With Ryoko (ally) and "arsenal strength" (spell) you can increase that DMG up to 25 DMG per turn. The old God Ithotu will increase your DMG aswell, so you might prefer the small candle with its fast speed over the scalpel, if you have that God selected. Similar to the Steak Knife it is possible to deal up to 30 Damage per turn with all aviable bonuses aktivated. Another perc is, that running from battle with the small candle equipped will only cost 3% Doom. You might use this early in the game or when facing anoying enemies like the burning man etc.
Ritual Dagger: Another useful, but expensiv item (4 Funds). It has decent Damage, Accuracy and Speed and is slightly better than the scalpel. Without the mentioned bonuses, this is the best Weapon for KNW-builds you can buy. It also gives you a special perc. Since it's so expensive, I prefer taking the cheaper Bone Saw, but this may just be personal preference.
Cursed Scissors: These are the Scissors used by the 3 headed Lady. You might have noticed, that she won't drop them. Obtaining the Scissors is not determinated by drop-chance, but by accomplishing the right ending. To do so, you have to draw the wrong sign on the board. This will cause the Scissor-Lady to be stronger. She will have 6 more HP, 1 more DMG and will be harder to hit. In exchange, you will recieve the Scissors. The weapon is very strong and has astonishing 6 DMG. The fight against the Scissor Lady is pretty hard tho and will cost a lot of STA and REA, if you are not prepared and have a low level. On the other side, when you fight her on the 4th or 5th mystery, you won't make much use out of the Scissors. This is why I wouldn't say, that you need the Scissors on every run. Just do 2 mysteries, and then decide, if the situation allowes to risk it.

Perception:
Beside the 4 aviable guns there are only 2 Perception-based-weapons: the army-knife and the torch. The army-knife has to be unlocked by completing an achievement. In the illegal den location, which has to be unlocked aswell, you can buy it for 4 Funds, pretty expensive, but it has a great mix of the 3 waepon-values: DMG, Accuracy and Speed.
The Torch can be found in the School, after you burned down during in the Mermaid-Mystery. I haven't tried this weapon, but it seems to be pretty decent. It also counts as a light-source, and the game treats it, as if you had a flashlight. One more reason to burn down schools while singing "another brick in the wall", I guess.
Guns:
Police-Revolver: Steal the gun of the dead police officer -> Random Downtown-Event
Hunting Rifle: Buy for 11 Funds in the illegal den (which I do not recommand) or get the ryoko ally (park ranger -> recruit during farout-festival) and let her die in a certain event.
Sport Rifle: Aviable in the school lockers (right locker), which can be opened with the small key, that can be obtained by fully investigating the abnormal-arms-mysteries (full investigation = Side quest).
Shotgun: Starting-Item of Moriko.

Conclusion:
Knowledge and Perception based builds aren't that powerfull in my opinion, since your "block- and dodge-action" will gain no benefits. KNW makes it easier to access spells through events though. In my opinion getting good spells is to luck-depended. Same goes for accessing guns.
What is the best weapon/build? It depends on your highest stat, your chance of obtaining a weapon and luck.
- If you can obtain the baseball-bat, the meat cleaver or the fire ace (reward for Ending A of Mermaid-Mystery) Strength builds are the strongest.
- If you can get Ryoko and the Arsenal Strength Spell or play against the Old God Ithotu, Dex and Knw Builds with either a Steak Knife or Small Candle are incredibly good. Even without these Options the 2 weapons are decent.
- If you have a lot of money at the start of the game, getting a Army Knife from the illegal den is a smart move for Perc-builds
- If you play as Moriko -> Your shotgun is your best friend

General:
On the combat menu, there are 4 categories of actions:
1. Offensive: Kick, Bite, Shoot Light Attack, Strong Attack, Prepare the attack, Boost the attacks accuracy by 10
2. Defensive: Run, Dodge, Block
3. Support: Let an ally distract the enemy, struggle (double damage of this turn if REA or STR is below 4), trade 10 exp for 10 accuracy, Meditate (trade 2 Stamina for 1 Reason)
4. Ritual: Clap and Bow, Offer Funds to deal damage, Cut ties to the world of ghost enemies, Pray (Trade 2 Reason for 1 Stamina)

When do you use which combat action?
I will not explain the basic math thing. I think everybody is able to calculate the most efficent order of attacking. But here are some tipps:

1. Should you run from battle?
Combat gives a lot of valuable exp. The more you fight, the less exp you will have. You will miss the chance of boosting your stats, and will more likely fail skill checks. It also rises Doom by tremendous 5%. This is why you shouldn't abuse the run-action. Other than that, this option can save your run, espacially, when you have the pocket-knife in your inventory, which will lower the cost of escaping combat. Still, you shouldn't run early in the game, where gaining Level is your primary goal.

2. When do I avoid combat?
Another option is to avoid Bossbattles. As I said above, it might not be that smart fighting the janitor, the horrible old man, the scisor lady and aka manto in a sinlge run, unless you have a lot of luck and perfect items, allies etc. Try to consider your ressources and calculate, if it's worth fighting a boss for bonus exp.
Example:
If I have 2 mysteries left, one of which being the Crimson Cape-Mystery, the other the Contaigous Coma-Mystery, and I only have 8 Reason left after taking a bath, I might not do the side-quest of the dream-devourer in order to fight him. I would avoid this boss battle, to stand a chance vs. Aka Manto and survive the upcoming Light-House-Events.

3. Dodge and Block
Against the listet bosses and bulky enemies in general you should be patient. Block or Dodge every turn, until the enemies HP are low enough to savely kill him with everything you got. Take the action which requiers less combat-time. If they take the same time, consider the type and amount of damage of the enemy. If he deals 3 or 5 damage, I recommand to block, since the value will be rounded down. If he deals 2 Damage, dodging might be better, since it is not that horrible, if you fail the dodge.

4. Call for help
Depending on the allies you have, you might want them to distract your enemy. This will boost your combat speed for the rest of the fight 70% chance. There is a 30% chance that your ally will die, without granting the bonus. Use the Dodge or Block action combined with the call for help. Don't be stupid and attack him with no guard. Often a distraction makes it possible to Dodge/Block, prepare and attack in the same turn. Sometimes you will have only 1 very important ally like Kana or Ryoko. You don't want to loose them! I wouldn't recommand calling for help, while they are in your team.

5. Finishing Blows and Guns
A efficient way of saving STA and REA is to dodge/block until the enemy is low on Health. As soon as he is go all in and finish him. Consider following Menu-Options to max out your damage:

- Throw an item -> Weapons, B-Slot items and bottles can be thrown during combat and will deal 0-5 Damage. You don't want to throw your only weapon or something like a flashlight. But saving up collected items for boss fights might be a good idea, which is why you should always start with easy mysteries and save the hard bosses for later.

- Send out an Ally -> Select a ally from the main-menu and send him/her out vs the enemy. This deals 0-5 damage. This is a good way of making use out of otherwise useless students. If I can afford the rise in Doom, I visit the school, get 3 allies and force them to join me right before a boss-battle.

- Use Guns -> If you have a gun AND bullets, you should only shoot to finish a boss. Shooting will give you the "ringing ears"-injury which slows down all actions until the end of the curret mystery. Also, you should prepare the shot. Risking to miss a shot will cost you a bullet and the enemy will get a free hit on you. It's absolutly not worth it, unless you would die otherwise. No need to mention, that you will need to equip the Gun before combat starts! If your perception is low, your usual weapon which fits to your main-stat might even be the better option, espacially if you don't have an ally which can support you with distraction.

6. Managing Reason and Stamina
Only forget spells, if you would die otherwise. If you have Funds aviable and can afford raising up doom, you can get meds form the farmacy to use in battle if the worst-case scenario occurs. You might fail to dodge or an ally fails to distract etc. Only forget spells if its necessary to stay safe.
FunFact: If you suffer under the "paranoia"-curse you can kill allies in order to regain 1 REA.

7. Prayers
Some enemies can be banished. Use a combination of 5 Claps and Bows. I recommand to take a pen and a sheet of paper and write down some notes like:
Clap Clap Clap Bow Bow -> 3 are right = this means 2 are wrong -> I have to change 2 Options
Clap Bow Bow Bow Bow -> 3 are right = This means one of the Claps was right, one was wrong.
Clap Clap Bow Bow Clap -> 5 right, looks like I was lucky and got the right combo.