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