Episodes
Here is the list of episodes Molly Shannon has appeared on in Will & Grace playing Val Bassett.

Grace, Replaced / Season 1 / Episode 18
When Grace's job forces her to work overtime, Will feels utterly neglected. He seeks solace in the company of a new neighbor, Val, a recent divorcee who matches Grace quirk for quirk. At first, Grace seems oblivious to their camaraderie until Karen warns her of impending danger.

Girls, Interrupted / Season 2 / Episode 20
Grace suspects Val may have stolen her music box and tries to convince Will that their neighbor is a kleptomaniac.

Last of the really odd lovers / Season 3 / Episode 21
Jack revels in the attention lavished on him by Grace's eccentric friend, Val.

Fagel Attraction / Season 4 / Episode 22
Grace is again hassled by her psycho neighbor Val who opens a rival design business and prospers by stealing Grace's ideas.