Can I create custom brushes in Toon Boom?

Hello! I’m looking to get Harmony, but I’ve recently been looking at Toon Boom Studio (without Harmony) and I was wondering if both programs have the ability to create custom brushes! I want to be able to create ashy looking brushes for an artistic/painting feel!

Is this possible? If so, how is this achieved?

That level of customization is not possible in Studio nor Harmony Essentials. You would need to have either Animate, Animate Pro, Harmony Advanced or Premium.