Pacman Ghost

Draw a Circle. Then with the Pen tool, click under the left and right points to add a point on each side. Drag them down with the Subselect tool til you have something like this...

Use the Freeform tool (size around 100), start clicking just below the bottom and push upwards a bit. Repeat on the other side.

1. Draw a circle for the eye - fill with white.
2. Draw a smaller circle for the pupil - fill with black.
3. Change the fill of the white circle to a Radial gradient, use the preset "white to black" and then change the black to a light grey.Position it so the white is behind the pupil.

When you've finished one eye, group the 2 layers (CTRL+G) and copy/paste and move it over.

Fill the ghost with an Ellipse gradient, black to the color of your choice (in my case green). Adjust the gradient handles as shown.

Highlight the top left corner to make it look like the light is hitting that part. Draw an Ellipse, fill it with white, soften the edges (feather or under Filter>Gaussian Blur) and reduce the opacity.

Add a shadow underneath - Ellipse, solid black fill, no stroke, feathered edge, reduce opacity.

Add a bit of texture to the fill. Here's an example with a different color...

Other examples with more details added. Just make sure if you add details, you use Vector tools/shapes...