Currently Decker seems to be able to draw with different brushes, but there's no difference at all in what's drawn, and this is discouraged by Decker switching away from the Fill tool on a change to the brush. So rather than an additional fill function, there's room in the design for the existing fill function to repeat the brush so drawing with different brushes would be useful.
Still, patterns also have animation and have this interesting effect: if you get a pattern into a canvas and move the canvas, the pattern reflects card coordinates rather than canvas coordinates. Paste this widget and move it around to see that:
%%WGT0{"w":[{"name":"canvas1","type":"canvas","size":[25,38],"pos":[282,72],"image":"%%IMG2ABkAJgAMGwUAExsHABIbBwASGwcADBsEAAIbCAAKGwYAARsIAAkbCAABGwcACRsIAAEbBwAJGwgAARsHAAkbCAABGwgACBsRAAgbEQAIGxEACBsSAAcbEgAHGxIABxsTAAYbCQABGwkABhsJAAEbCQAGGwkAARsJAAcbCAABGwoABhsTAAYbEwAGGxMABxsSAAcbEgAHGxIABxsSAAcbEgAIGwgAARsIAAgbCAABGwgACBsIAAEbCAAIGwgAAhsHAAkbBwADGwUAChsHAAQbAwAMGwUAFRsDACY="}],"d":{}}