Diana, on occasions where she has to save a possessed Martin from something. For someone who is usually the Damsel in Distress, she does a very fine job of stepping up to the plate when necessary.
Season 1
In "Attack of The Sandman", Martin, Diana, and Java overcoming their fears and escaping the nightmare realm with the other captives from Sandman.
Season 2
"Crypt of the Djini" where Martin stops a massively Jackass Genie that actually forces people to make wishes according to their greatest desires, so that she can twist them around to screw them over. She already pulled this trick on most of the cast, but when she tries it on Martin, she runs into a speed bump because Martin's wish is to know how to save his friends. She knows that he found out how to seal her and tries to tempt him into making a selfish wish, but Martin beats her tricks through Heroic Willpower and wishes for her to be sealed back up.
Martin reverting Diana back to her original personality in "You Do Voodoo" by using a blank paper.
Billy's true form is this, with a touch of Nightmare Fuel.
Season 3
In "Curse of the Looking Glass", Diana is trying to convince "Darlene" (really Darla transformed into a 'pretty girl') to reverse the wish she made on the titular looking glass. With all the professional insight of a school councilor, Diana gradually tells Darla that she doesn't need her Darlene-persona to get a guy to like her, whilst they're running from the monsters the looking glass created.
In the same episode, Billy (under the guise of a human being) gives advice of his own that finally convinces Darla to reverse the wish.
Diana: The next time, that someone could be you, all it takes is confidence.
Darla: What if he says no?
Billy: Then he's an idiot. Because I saw the real Darla in the picture. And she's beautiful.