Typically starting off, you can hunt and sell 100 uses of food for 1gb and save that up.
Selling event items during the month is a way for quick GB, however keep in mind they do sell for more down the road

As for customs, there's some "uncommon" bases you can give a custom lioness; like Onyx, Xanthic, etc
Custom Bases Uncommon on the Wiki
^ that's the full list of bases you can use when creating a custom lioness in the Oasis
Uncommon work practically just like rares except rares are breed only and not applicable.

Mutations are typically bred. You can stud out to kings with mutations for a chance at getting one; lower fertility girls work best but keep in mind people have minimum fertilities they'll stud to since 1-10%s can be difficult
There are ways to apply mutations; these are called Mutie on Demand applicators. The Piebald ones are very expensive but available during Black Friday if you purchase GB.
The Primal on Demand applicator is a much cheaper option; it can't be applied to females however.

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Additionally to what I said about studding out for mutations; some mutations aren't passable from kings.
The passable ones are piebalds, patches and primals. All variants of those c:

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Ok, thank you so much for your help! :)

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Where do I get the mutie on demand applicators? And when do black fridays happen? Thanks so much!

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You can get muties on demand from user's branches, or the trading center. They go for more via the trading center than users branches, so I suggest saving up for one and buying it from a branch.

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Thanks for the heads up, Wei Wuxian! I appreciate the tip! :)

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