Ursula gets a mini reprise of Poor Unfortunate Souls while in her human form as Vanessa, and it is her use of her stolen set of pipes that tips off Scuttle (and then Ariel) to Ursula's schemes. What makes this song thrilling for us the viewer is the opportunity to hear Jodi Benson villain it up, complete with maniacal cackling at the end. This song is brief, but delicious.
As far as I'm aware, this song wasn't part of any of the official albums until 2014, when it was included in the Legacy Collection soundtrack. Funnily enough, the album's booklet credits Pat Carroll for this song, not Jodi Benson.
What a lovely little bride I'll make, my dear I'll look divine
Things are working out according to my ultimate design
Soon I'll have that little mermaid and the ocean will be mine