Check Use color from gradient.

Select the Clone tool and set the source to “Maple Leaves” pattern.

Use Filters → Render → Pattern → Grid to create a grid. Use the Smudge Tool to draw a line with a slightly larger brush.

Use Filters → Render → Couds → Plasma to create the cool plasma cloud. Use the Erase Tool with a square brush to draw a line.

Use the rectangle select tool to select a rectangle, and then fill the selection with a light blue color. Select the dodge/burn tool. Set the type to Dodge and paint along the top and left side using an appropriately sized brush. Set the type to Burn and paint along the right and bottom.