Ice Beast

[This content is for mid/late-game players, like who wants to craft Homunculus or Reappraisal stones.]

This Beast is not extreamly difficult to beat. His special ability is “Freezing Air” and it freezes 75% of the MAX HP. The frozen HP will be substantially recovered proportionate to the increased amount of Attack Bar.

FRONTLINE:
Like in every other beast, you will need Attack buff! That’s why I recommend you to use colleen or chasun (both are good, but colleen gives 3 turns Atk+ / beside chasun heals and tanks more).
As second front liner a tanky Bernard would be optimal, because he gives Speed buff, and for survive this Buff is substantial.

BACKLINE:
You can really use what ever you want as damage dealers. Lushen, Lagmaron, the blue/yellow twins, Sigmarus, Theomars, Taor.. Every good Wind and Water single target damage dealer.

Wind Beast

[This content is for mid/late-game players, like who wants to craft Homunculus or Reappraisal stones.]

This Beast has a horrible passive: he applies “Electric Shock” (the damage you receive will increase under the Electric Shock Effect. The recovery amount you receive will be decreased by 50% and you’ll be inflicted with Continuous Damage proportionate to 10% of your MAX HP every turn. You must reach 100% HP in order to remove this effect).

FRONT LINE:
That’s why you should bring at least 2 healers here: Colleen/Hwahee (that heals and grants attack buff) and a second healer like Belladeon (or Louise if you got):

BACK LINE:
In the back line you should put 4 fire damage dealers like Trevor, Laika, Shihwa (all recommended in vampire) and Brandia if you have. An other very very very good unit for Wind Beast is Perna, she is an awesome damage dealer and helps a lot with heals.

Good luck !!

Fire Beast

[This content is for mid/late-game players, like who wants to craft Homunculus or Reappraisal stones.]

This Beast is easy to beat since you have AoE damage. It spawns 8 fire minions and you should kill them before the Beast get another turn, or they will explode on your team and kill you.
You should bring at least 2 AoE mobs, like Lapis, Taor, Zaiross, Shi hou or Brandia for example.
If you have Brandia you should put her in the team 100%, because she has AoE damage (2° skill) and is the best single target damage dealer in the game (her 3° skill is really awesome).
Let’s talk about what is needed. Definitely Atk+ buff and Def Break, if you got Brand is optimal.
The best attack buffer is Colleen, which you can use in frontline, and she will be your tank/support/healer.
As second front liner you can use a water damage dealer (takes -15% critical hits from boss) or a hybrid support like Anavel (with +950/1000atk she is able to kill a minion wave with 3° skill).
In the back line you just need to go with 2 AoE and 2 strong single target damage dealers (Talia and Sabrina are the top).

Is not that hard 😛

Good luck