If gold fills up, it transfers automatically. This skill is the most Over Powered in the game because it helps you earn huge amount of gold specially if you let the app run and leave your phone for a long time. There are two ways to exploit this skills and you can do it both at the same time. Any warrior that attacks an enemy. You can gain from the weakest 6 gold per enemy to 100+ gold for stronger boss you can kill. When you have this skill, you don't need to tap the coin icon because it will automatically transfer to your coin bank. The only problem with this is if you leave your warrior, it might die. So putting it to a lower level that he/she can survive. Fortunately you can buy an "auto skill" that cost 250 gems. If you have an auto skill then aid your warrior that has a gold passive skill with another warrior or warriors that has a healing skill.

There are two miners available that has a Gold Passive Skill: Pro Miner and Legend Miner. For Pro Miner, you should put it to lower levels if you don't have an auto skill because it won't survive since he cannot attack enemies and enemies will attack him. If you have an auto skill, partner him with another warrior or warriors that has a healing skill for him to heal and attack the enemies. For Legend Miner, you don't need to any warriors to help him survive because he has a passive skill that he cannot be attacked by any enemies including the boss.

You should only upgrade this based on your Gold Mine capability. Gold Mine has 3 levels of mine: Small Mine, Middle Mine and Big Mine. For example, if you can mine the Small Mine in it's allotted time, you will get 8000 gold, so you should upgrade your "Increased possession amount of gold box." above 8000 but not greater than 10000.

Upgrade this to be able to swap warriors easily. This is important because you are only limited to 3 warriors in enemy field. Putting the warrior in a slot condition will recover it's lost HP. The faster, the better it is. So you can have 3 warriors in the field most of the time.

When you upgrade this, all of the warriors inside the field will receive a damage boost. This is useful when it comes to missions that requires fast damage such as Gold Mine. However, don't upgrade this too much because it will be much more expensive and it is better to upgrade your warriors first because it is much cheaper. But if you have max level of all of your warriors then you can upgrade this as soon as possible.

This is very useful if you have a miner warrior class. However if you want to upgrade this, you should have atleast a Rank A or B miner warrior class because lower class has also a lower gold capacity which means upgrading this is useless.