All the enemies are front line attacker. So, use the plus formation like shown on the video . On this battle use heroes who have a skill that attack the “+” formation such as Tart, Tiurel, etc. This way you can kill them all quickly.
Put one hero on top and bottom to absord damage from the pierrot. Your priority on this battle is to kill the earth god ASAP (use strong single target skills, example: Crima, Cheon, etc) while keeping your top and bottom heroes alive. Have a nice healer such as Melia will helps a lot.
There are 2 dwin, they have a lot of health. Choose a hero that can attack the backrow or even better attack all of them (such as the elemental).
Formation: place one tanker on front column because dwin’s skill target the first column, this way dwin will only attack one target. You can also put 2 heroes on bottom and 2 heroes on top to kill the elder ruby ASAP.
There are 2 Tiurel on this battle, so make sure you not use the “+” formation. For the formation I suggest you to use “X” formation. Use strong hitter that has a skill to attack the front line to kill tiurel and Ramia quickly (example: Cheon, Frost Wolf, etc).
Many players have trouble on this floor. First of all, the important thing you need to pay attention is your formation, avoid using “+” formation because bomber’s attack have “+” AOE. You can use “X” formation on this battle, so bomber’s attack only affect one hero.
Your first priority should be Madeline because she can heal everyone. If you want more attack power then you can put 2 heroes on top and 3 heroes on bottom. It’s very useful to have a hero that can block continous damage buff (example tree giant, etc) in order to prevent the burn damage.
After killing Madeline you can focus on Sven or other heroes. You may want to re-try this battle few times, if you die, because sometimes bomber get a critical hit which will interrupt the battle.