With Lasso Fill, you can easily fill in the area you have boxed in with the lasso. In this example, we will give the character a "cartoon-like" shadow.

Open ①Layer window. Tap ②Add Layer to add a layer. Set ③Blend Mode list to "Multiply".

Open the ①Tool Select window and tap ②Special.

Open the ①Special Pen window and select②Lasso Fill. Adjust ③Opacity as you see fit.

Box in the area you want to add the shadow and fill it in.

Finally, open ①Layer window. Select ②shadow layer and click ③Clipping.

And we are finished!