S8, E6: At Monica's Halloween party, Phoebe meets the friendly fiancé, Eric (special guest star Sean Penn - "Dead Man Walking"), of her flighty twin, Ursula. Phoebe becomes alarmed when she learns that her sister has misrepresented herself to the trusting guy--and Phoebe finds herself attracted to him as well. Monica comes disguised as Catwoman and wonders if she could defeat Phoebe's Supergirl character. Chandler arrives as a pink bunny and mistakes Ross' giant "Spudnik" costume for something found on a sidewalk. Also, Rachel gives away all the candy and guiltily resorts to writing checks for the trick-or-treaters.