The serial plotter draws nice curves along a time axis. It would be nice if there were an XY-plot function. Say a PWM or a DAC pin would output a varying value (oscillating f.i.) between 0 and 255 to a circuit and an analog input pin would read the response from the circuit.
The output value would go to the X axis and the input value to the Y axis. The plot could reveal interesting things, things that the normal plot wouldn't.
Since this kind of plotter doesn't scroll with time, it needs options about how the trace should fade from the screen.
Make your code draw the top half on one trace and the bottom half on another trace. For example, make trace 1 draw (pi to 0) and trace 2 draw (pi to 2pi). Nothing is stopping you.