The song shares many similarities with Ursula's "Poor Unfortunate Souls" in The Little Mermaid, both being sung by villains who claim to do business by helping make the dreams of others come true when in reality, they're doing what they do for their own benefit and delight, and both are used as means to deceive the protagonists (both, coincidentally, being royals) into making deals with them, and both songs ending with the protagonist undergoing a mystical transformation that will last for nearly most of the film.
Facilier pleads for both of them to shake his hand, and grins evilly as they do, sealing a contract with him and summoning his "Friends on the Other Side", who take the form of voodoo dolls, masks, and shrunken heads.
Retrieving a talisman from the largest mask Friend, Facilier uses it to prick Naveen's finger and take his blood, starting his transformation.
Lawrence is terrified as his master shrinks down into the form of a frog, as Facilier exults with dancing and fireworks with his friends saying that they got what they wanted but lost what they had, before the camera fades to black with a warning of "Hush..." from the magician.
Upon doing so, Facilier falls into a state of immediate panic and frantically tries to recollect the pieces of the broken talisman, just as his "Friends from the Other Side" arrive, announcing their intentions to collect the doctor's soul as punishment for his failure to repay his debt.
[2] Slate wrote "[Facilier's] big number, Friends on the Other Side, is the best-written in the movie and a great showcase of spooky, voodoo-inflected animation; his comeuppance is appropriately spectacular.
"[3] High-Def Digest wrote "Pixar stalwart Randy Newman... adds warmth and a wonderful sense of genuine Americana to the proceedings...
It's a tune that's a devilishly fun match for Danny Elfman's "Oogie Boogie's Song" in The Nightmare Before Christmas, let alone when Alan Menken had Ursula belt out "Poor Unfortunate Souls" for The Little Mermaid".