what is the easiest way to get money?

I like to send my pets out on missions, it takes awhile depending ont eh skill level of your pets but I tend to get quite a bit given some time

The most reliable source of income is missions and they also give other benefits such as experience for your pets, pet gear, and elixirs. They also require fairly little effort. If you need advice on getting started with missions, there are guides about it. Another way to earn gold is to nurture lots of sylestis for scales and the chance of an essence. The essence can be sold and if you earn enough scales, you can buy and sell a lesser genetic mutator or lesser pet dye. Selling pets can also bring gold but is unreliable at best. Another option is to battle a lot and sell the gear you get from that. It is generally a small amount but it can give you a boost.

Hope this helps!