Level 80

This is the eighth boss on the Adventure Map and the first stage with all three waves having a full team.

Strategy
What makes this stage painfully hard is the fact that the Goldcores can heal each other and gain Regeneration. This is very annoying since they have very high health. On top of that, they are immune to Stun, making sure that denying them is hard.

Strategy 1 (ft. Evaranae)
Monsters: Evaranae, Goldfield, a strong Metal or Earth attacker

Moves: Evaranae needs Mortal Bite and Regenerating Bite

Runes: 3 Team Speed on Goldfield; 2 Life and 1 Speed on Evaranae

What to do:

Let your attacker kill the Raanes in the first wave. Doing this shouldn't be hard. For the next wave, do the same thing, except leave one Pulseprism at decently low health and keep him in that state. While he is at low health, make sure your team is at full health. When your team is ready, let Evaranae finish off Pulseprism with Regenerating Bite. You should now be in the final wave. Let Evaranae use Mortal Bite on the biggest Goldcore. He should now die in 3 turns. His teammates can't do anything about it since they don't have NER. Once he dies, make sure Evaranae gets two turns in so that she can use Mortal Bite again. Make her use the skill on one of the Goldcores and repeat the process one more time.

Strategy 2 (ft. One-hit wonder Jakugan)
Monsters: Jakugan, Goldfield, any third monster

Moves: Jakugan needs Head Crop and a low damage move. Goldfield needs Aether Fusion and Righteousness

Runes: Jakugan needs enough Strength runes to have a power of 4356. Goldfield needs 3 Speed

What to do:

Jakugan's high power can be enough to kill literally anything in this stage with Head Crop including the boss if she has Damage Boost and Double Damage applied by Goldfield at the same time. Kill the Raanes in the first wave as quickly as possible. Then you should be in the Pulseprism wave. Kill two of the Pulseprisms and chip the health of one of them off with Jakugan's low damage move until he is at a low health stat. Let Goldfield apply Damage Boost and Double Damage on Jakugan with Aether Fusion and Righteousness. When she has the required buffs, kill the Pulseprism and move on to the final wave. Let Jakugan kill the boss with Head Crop. Now you should be safe. Just do the same thing you did with the boss on the other Goldcores.