To beat the hardest bosses of this game, you need a lot of preparation before to even try...

I leave here the quick list of what to do, and in specific sections, explained in more detail:

1. Reaching to Level Max
   
2. Getting the Equipment
   
3. Improving that Equipment
   
4. Getting Rockets, Bahumot Summon and more
   
5. Fighting and beating Koohii
   
6. Fighting and beating Seraph

First we have to Level Up our characters to the 'Max Level', but in this game there are no levels as such, I mean the 4 main characters, have all learned his Skills and Spells:

• Slayer V
  
• Guardian V
  
• Thief V
  
• Elementalist V
  
• Trickster V
  
• Healer V

Depending on your decisions, your characters should have between
3500 and 4500 HP approximately, in addition to its rather high statistics, but still not enough...

To getting the Skill Points needed, the 'fastest way' is fighting in the Battle Arena,
in particular, the last one, the hard difficulty Snowy Chillers normal enemies

Only Spam the Skill 'Shockwave' use Quicken All
to get additional Speed and Heal the group if is necessary

At first it is perhaps difficult or slow, but over time it will be a
matter of 1 or 2 minutes to win the battle and win many SP and money

You will earn 48000 SP and 16000 gold and with luck, Equipment and Rare Items

You will need that Rare Equipment, if you want to increase the rarity of these Items,
equip with at least one of your characters with Equipment 'Dice' to increase your luck

One of these Rare Equipment would be the SP Ring,
with him, you double the SP you win in battle

You will need approximately 4 million SP for your characters to reach at Max Level

In my opinion, this equipment is highly necessary to achieve victory in these two fights,
is the only way to increase your statistics beyond the Maximum Level and in the case of
two of them, increase certain statistics do not increase with the Level Up

This is what you should get:

• Wapons of Level IV x4
  
• Circlet III x4
  
• Full Armor IV x4
  
• Armor IV x2
  
• Monocle x2

- Weapons of Level IV are obtained after improving your equipment with Scrap Metal,
it is necessary because you increase your stats; Attack, Magic and Speed
Furthermore, you can also access to the special techniques of Level 3 of your characters

- The Circlet III is like you equip at the same time; Gauntlets, Amulet and Boots Amulet,
I would recommend you improve at least to Level 10, but you can reach up to Level 21

- The Full Armor is mandatory to improve to the Max, the Level IV Full Armor at Level 11,
so you will increase your Physical and Magic Defenses permanently in combat by 35%

- The Armor IV would have to Equip to your Healer character and the other character
not Equip with the Monocle, this will increase your health by 1000 points at his Max Level

- Finally, the Monocle, you will increase your Critical Ratio Chance by 25%,
this Equip should give to your physical attackers and use Skills than hit more than once,
so each impact can have a chance to result in a Critical Attack

You can craft them in the store, in the alchemy zone,
with the items you indicate there, but the following Bosses maybe drop it:

- Armor: Is Easy, you can buy it in many Shops

- Circlet: Bat King, Mummy King, Zombie King, Queen Slime y Samurai King

- Full Armor y Monocle: Fighting again in the Battle Arena, the Snow Chillers maybe will drop these Equip and the other I say before, remember, Equip the Dice to increase the chances

At the end it will be something like this, but once improved:

To upgrade your weapons and equipment you will need maaaaany Metal Scraps,
although initially asked few units, in higher levels they will be asked many more,
so you'll need a lot of money, because although they can be obtained in many ways,
the fastest is by buying them in stores, but I recommend you do when you get The Neck Tie,
as this will reduce its price by 25%, and each unit 75g and not 100g,
so when you buy 99 to 99, it will cost 7450g and not 9900g

In addition, you will need several Gems to increase the power of Weapons and Equipment
once they reach the Maximum Level, now I will show how to get and where to get the Gems:

• The Esmeralds and Amethysts can be buyed in many shops in the games in 1000g/750g each
  
  
• The Topaz and Aquamarines can be Stolen at 100% from the enemy number 137,
  Birdo, can be found in the 'Aurora Island', sometimes gives Topaz and sometimes Aquamarines
  
  
  
• The Sapphires and the Rubys don't will appears until you beat the Chapter V,
  you can get them in the following places, doing the next tasks:

* Sapphires:
- One of the Rare Items to fish in the area between the Light Tower and the Lao Prison
- When you get the Generic Items in one of the chest of the Generic Quest
- Possible Item if you beat the Extra Stage in the Mercenary Defense (only a 2% of chance)

* Rubys:
- You must get a Gold Medal in the Track 3 of Snowboard Xtreme, you win a Ruby
- When you beat the Boss from the Generic Quest
- Possible Item if you beat the Extra Stage in the Mercenary Defense (only a 2% of chance)

Whatever I said, fighting in the Battle Arena, the Snow Chilling, these Gems maybe will be drop, but I recommend again Equip a 'Dice' to increase the chances of happen

Finnaly, to gets a lots of money, is in the same place, fighting with the Snow Chilling in Hard
You win 16000 gold each time you beat the battle, later you can sell your Gems,
but first, get the Gold Medal in the Track 2 of Snowboard Xtreme
to get the 'Gold Paint', to sell the Gems for more money

The guide for the Generic/Secret Mission:
http://gtm.steamproxy.vip/sharedfiles/filedetails/?id=471755246

And to finalize preparations, it would be advisable to get the following items,
it will help you a lot to overcome the fights and not make it too long...

• Rocket x 20-50
  
• Bahumot x2-5

The first is fairly easy to get, the last normal enemies usually drop Rockets and you found some in the Chests and again, you will gain some fighting withe Hard Snow Chillers in the Battle Arena, I recommend that you keep the Rockets to these two final battles

The Rockets must be used by your/your characters with more attack and equipped with the Monocle, so each impact (of five), it will damage between 2500 and 7000 HP each impact,
depending on how many criticals land achieve on them

Bahumot is a Summon and it more harder to get, as you can only steal to theown Bahumot or maybe dropped by itself when defeated, but this Boss is much more difficult to beat,
but it is good to 'test your strength', if you can't beat him or you beat him with complication,
or use many Items, you are not ready yet to deal with Koohii or Seraph...



When you use this Item/Summon all our characters gain the following effects:



Really, this is a quick way to get 'in tune', when you fight them and the battle goes against you...

This is not necessary, but is a good idea to reserve your Full Revives and the Elixir Brew II
and make some Panaceas withe the Alchemey (Grenade + Cure Potion)

Because it is more faster healing with Items that with Magic, so we have more turns to act

Finally, use your characters all single-use Items that increase our statistics that have been accumulated during the game, (Stat HP, Stat MP, Stat ATK, Stat MAG, Stat SPD, Stat All)
Try to make a 'fair' distribution between your characters,
either strengthening or balancing them further where they are good

Well, it's time to fight with the strongest Bosses, first Koohii, here her Stats:


As you see, her Stats are really high, especially in HP and Speed, so be patience,
the fight will be very long, so, my recommendation is that you Nerf her with:



She don't be so fast now and you will have more time to attack and heal, poison damage is not very high at first, but eventually, you will be able to make approximately 5000 to 10000 damage

Use on your team Quicken All to speed up the party

If you can, use on her and use
on your Strongest character before you attack her with Rockets

Try to make all your characters have , and her attacks will not be so hard

Mari must use Regen All, as soon as possible,
so you'll have to Heal less during combat and the Healer must have activated to Heal better

During this fight, go preparing your Specials Moves of Level III,
but don't use them until hes second transformation

Restore your Buff and her Nerf when they go away, but the Nerf only if she is still with high HP,
when she is beaten her first time, she will be cured of all Nerfs, don´t do it if >10000 HP


After rip away that large amount of HP, now her tranform in a gigant Koohii,
her HP will increase to the highest in the game, 220000 and increase its Attack and Magic almost
in 1000, although it will lose some Speed in this process, but I still recommend continued use:



Use again the strategy explained up to keep everything well, try the to heal quickly the party
with Heal All, Holy Light, or in an extreme case (you are with low HP and her will attack soon) uses the Brew Elixir II to heal the whole group quickly

Summon Bahumot if you wanna get a quick Buff of all lost it

Now is when you must use you Specials Moves
of Level III if is possible her with and you with

The most hard thing in this battle, is Koohii is immune to the Stun Moves like Barrage,
use the Rockets instead to do a massive damage on her, more if you land some critical hits

If you follow this strategy it is a matter of time
you beat Koohii an earn the Achievement 'Doom Bringer'

And finally only left Seraph, here are her Stats:


You see, in its first form is more faster and more powerful than the first form of Koohii, in her second for, only overtake Koohii in speed, so, that makes it Seraph really dangerous is its speed, as if hit all with Magic and you don't have enough time to heal...

Then, is mandatory use again with this, her Speed decreases 50%

And use on her again

The Big difference with Koohi, is Seraph can be with Barrage,
if you have luck you can her and get some extra turns

Practically use the same strategy with Koohii, poison her and lower her Physical Defense before launching Rockets with your Enhanced character and prepare you Special Moves of Level III and
use it in her second form, which is more dangerous

If you win this Battle you earn the Acievement 'Judge'