So is there a spcific sheme how to built a division ? like what characteters should i combine, should i watch for Leader Links and the order (from left to right) in which i built and arrange my Division?
How Important is Formation fitting the troops( like only Blader & Destroyer)or should i just switch the Leader every fight to get the maximum out of the Rock, Paper & Scissor.
Can/Should i lose some Missions for Grinding Purpose? How Important is it from the very beginning to equip every troop i hire (only the one with red smileys) with Tacticas?
I also found this, seems promising but still leaves many of my questions open
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There are things I agree with in that guide you linked, and things I disagree with... but some of it is also a matter of how you enjoy playing the game and all that.
I will say that there are posts in this thread that go pretty in-depth about division building, and a number of other subjects you asked, but I'm too lazy to search through the 50 pages again to find all of them. You'll have to do that yourself.
Some short answers, however are as follows:
When it comes to Division building, the first thing you need to understand is that outside of the Easy Difficulty, and even most of the time there, the AI always tries to target to unit with the lowest Effective HP, this doesn't mean the unit with the lowest HP, but the unit with a certain combined value of HP and Defense that is lower than the rest.
This means that Division building follows several rules:
1. Know which unit the AI will try to target, or intentionally add a unit that the AI will target if at all possible. This 'bait' unit can be many things, but usually you don't want it to be a primary attacker or anything important.
2. Have a Defender unit protect this bait unit from attacks. The easiest method is to put a weak unit as the 1st unit, and a Defender with Forward Guard right behind it. However, as you learn more, you can vary this quite a bit depending on what you're going for.
3. For the above to work, you also need Nulls. This game has area attacks. Pierce/Wide/Cross/All. There are corresponding nulls which make those attack only hit one unit. So there's Pierce Null, Wide Null, Cross Null, All Null, and Surround Null. Surround Null is the best one, and most rare one, which basically covers all area attacks in one skill. You can get the same effect if you have Pierce Null+Wide Null+All Null. Or Cross Null+All Null. These do not need to be on the same unit, they can be on different units.
4. There are also special attacks that need Nulls. Range Attacks, which can hit the backline, and Flank Attacks, which can also hit the backline, with some extra gimmicks. The skills Range Null and Flank Null cancel this. How much you need either of them depends on what bait you're using and where you put it, but on average, it doesn't hurt to have both of them in many formations.
5. Then there's the special effects. Atacks can have all sorts of debuffs like Charm/Stun/etc. These can be stopped with various cures, but generally speaking, Absolute Cure is common enough that it's not hard to get it on multiple divisions. If my memory isn't failing me, you even get one unit with it on your first Playthrough from the very start.
6. Other effects. There are special skills like Spells (or Blasts) which do damage to your units at the end of turn, these can be mitigated for a division with the Spell Barrier skill. Enemy Units with the Self Destruct Skill will damage your units when they die. The Self-D Barrier skill mitigates this. Enemy units with the Shelling Skill will damage your units at the start of battle. The Shelling Barrier skill mitigates this. There's also Tactical skills, and there's the Strat Barrier to mitigate those. For high-difficulty divisions, you want at least some of these at 100%, often Spell Barrier/Self-D/Tactical with Shelling being pretty important too. It's impossible to cover all of these though, so which is more important will depend on a lot of factors.
7. Synergy. You absolutely want a division to have synergy if at all possible. 'Boost' and 'Command' skills boost the stats of every other unit in the division except for the unit who has the skill. This means that it's extremely important to have synergy at higher difficulties. There are some exceptions though as the 'Boost Division' and 'Command Division' skills exist on some units, but they're usually weaker than skills like 'Boost Dragon' specifically because they can affect anything and everything.
8. Fool's Lie/Terrain Null. Fool's Lie is a skill that makes a number of skills unavailable depending on the number of the skill. So for example, Fool Lie 1 makes the 1st skill of a unit unavailable. Having Fool's Lie on your side can make battles significantly easier. If the Enemy has it, it can make battles harder or even impossible. If both sides have it, the side with the highest value gets to affect the other side with the difference. So if you have FL1 and the enemy has FL2, the top skill of all your units in the entire Battalion will not work. Terrain Null negates Fool's Lie completely, along with all the Negative Effects of Terrain too. I doesn't matter which side has it, if it's on any unit, Fool's Lie won't work.
With all this in mind, the typical division should have 1 bait unit, 1 defense unit, about two strong attackers and 2 utility units. Though there are more complex combinations in mind as well. How much everything else matters depends on the difficulty. On Easy, you can be a lot more lenient with stuff like barriers and Absolute Cure, but you don't want to ignore them completely.
In my experience, Formation doesn't matter that much tbh. On Easy and Normal you can completely ignore it and set the Leader based on which unit has the most convenient Leader Skills. Given that important skills like Fool's Lie and Terrain Null are often Leader Skills, you'll often have to take that into account when choosing your leaders. I've played up to Hard Berserk 5 and I finished Onikage's Ambition on basic Thanatos, and I can say that in both of these cases, Formation didn't play an important role in any battle. It can help, but, it doesn't seem like a decisive factor for anything other than maybe Thanatos B+.
My recommendation for the 1st Playthrough is as follows:
Play on Easy, use that time to familiarize yourself with the mechanics and experiment. Also use the scene collection guide linked to the 1st page and play through Law Normal, it's the easiest Playthrough, and it also unlocks a lot of Tactica, several Guest Commanders and titles for all of your primary commanders including Leon and Anora. It also lets you get Awakened Leon, which is a very good unit that is more flexible than Dark God Leon...even if I like Dark God Leon more and think that he's the stronger attacker unit between the two in most circumstances.
Rush through the 1st Playthrough as fast as you can. Don't bother farming yet. Figuring out the game is more important, and farming works better later anyway. New Game+ Allows you to start with ALL of your unlocked units and commanders, all collected items, and a bonus of 1 mil Gold and 1mil Magic. This makes it much easier to recruit and experiment on following Playthroughs. I recommend to keep playing on Easy after that until you unlock more things, and until you finish upgrading the Internal Affairs stuff. Yes, they have a maximum value. Also, Military and Healing have a cap that can't be exceeded even with Internal Affairs skills on units, so be mindful of that as well.
I'd recommend initially just using the scene collection guide to do ~4 Playthrough to collect most of the stuff. Don't bother with the save back-tracking thing, there's no point since you'll want to keep unlocked units. By that point, you should have a lot better grasp of the mechanics and you should be able to start experimenting more heavily with division building.
Until then, don't bother with titles on non-commander units. They're not really worth anything at the start, and you won't really know how to make the best picks anyway. There's no point in wasting Tactica for that when you'll need it to recruit units anyway, and you will need to do at least some recruiting, even on Easy. Even if ~4-5 Divisions are enough to rofl-stomp the game on that difficulty even before you fully get all the mechanics.
I genuinely recommend taking the time to read through all of the thread. You'll recognize the more important posts by the simple fact that they'll generally be Walls of Text, sometimes with Quotes and Spoiler Tags and whatnot in them. I also recommend grabbing ShinV's spread-sheet that's linked in his Signature. It has quite a bit of useful stuff in it, especially the Treasure Hunter breakpoints and stuff that will be useful when you're ready to start messing around with TH divisions.