This is my own strategy. You can modify it to suit you.
A. Things you need to prepare for the battle:
a. ≥+7 Plate Armor or ≥+9 Scale Armor.
b. ≥+2 tier-5 melee weapon.
c. ~10 Potions of Healing (well... Actually, if you use good armor early, you won't need to spend too many Potions of Healing before the Yog-Dzewa battle, because even dwarfs can hardly deal you more than 5 damage per hit if you have good armor).
d. Some Potions of Invisibility and Potions of Shrouding Fog.
e. >4 Potions of Toxic Gas.
f. Some Scrolls of Rage or Stones of Aggression (they can be created in an Alchemy Pot using Scrolls of Rage).
g. Recommended to have:
– A Wand of Corrosion.
– An Ethereal Chain.
– Some Scrolls of Teleportation.
– Some Scrolls of Retribution.
– Etc.
B. During the battle:
a. Use Potions of Healing if your health is low (obviously).
b. Use Potions of Invisibility and Potions of Shrouding Fog to get rid of Evil Eyes and Scorpios, as well as all enemies in the battle.
c. Throw Potions of Toxic Gas at Yog-Dzewa.
d. Throw Stones of Aggression at Fists. This will force surrounding enemies to attack these Fists, and also help you avoid damage from Evil Eyes.
e. Etc.
C. After the battle:
If you can survive until then, so... congratulations! You won!
(Fortunately, Succubi won't appear in the battle. If they did appear, the battle would become a nightmare).
Demon Spawners are enemies that spawn in the Demon Halls and look like red balls. They are connected to Yog-Dzewa—the final boss in the game. If the Badder Bosses challenge is disabled (which can be enabled by clicking the gear icon in the hero selection screen), each Demon Spawner will give Yog a 25% chance of spawning a Ripper Demon instead of a God's Larva, but if the challenge is enabled, Yog will also spawn Evil Eyes and Scorpios if Demon Spawners are alive. To get this badge, you need to kill Yog without killing any Demon Spawner.