Well, this scene is going to take heavily from "Castlevania: Order of Ecclesia", specifically, the
revelation that Barlowe is the true enemy (As well as the resulting boss fight therein).
. Also, it will explain some details as to how Ariel's dress disappeared, as well as some other intricate details.
As Ursula drags Ariel down the depths, Ariel eventually yanks free. Ursula then tries to goad her to come.
"Ariel, come to me... Allow me to pronounce the final acts of the bargain, become mine! allow the ocean's greatest hope to rise, in your close victory." says the Sea Witch in an eerily calm manner.
Ariel, after realizing Ursula's deception, her guilt for even going through witht he bargain, as well as Ursula's underhanded tactics throughout the three day period, has had enough, and stands up to Ursula, not caring whether she has to face the consequences.
"I will not!" Ariel angrily shouts.
Ursula is mildly surprised at this, as none of her "clients" directly refused to be sacrificed. Still, she retorts trying to goad her into becoming the penultimate sacrifice, calculating Triton's arrival, so he will be the ultimate sacrifice.
"What... Second thoughts? You fought to experience the human world fully..." Ursula says.
"I realized the error in my ways after hearing from Scuttle about what you did, I'm not going through with it." Ariel responds.
Ursula curses to herself, realizing now that she should have killed the Seabird when he overheard her conversation to the dark demon of destruction, as well as her own plans. However, she's still confident of trying to get Ariel, this time by trying to trick Ariel by claiming that Scuttle is nothing but a compulsive liar.
"Scuttle told you? He must have lied to you...." Ursula starts.
Ariel cuts in:
"You would know quite a bit about lies, Ursula!" Ariel says angrily.
Ursula is surprised at Ariel's claim.
"Ariel, What's is this? What do you mean?" Ursula says with slight anger.
Ariel remembers the incident at the mangrove, and remembers that she saw a bit of flotsam and Jetsam's eyes underwater while being helped up by Eric, and realizes they were the ones who capsized the boat.
"The Boat didn't capsise by a freak accident, you sent Flotsam and Jetsam to capsise it so I wouldn't try to kiss Eric, and you lied about interfering because of that!" Ariel points out.
"R... ridiculous, I've never heard such--" Ursula starts to retort angrily.
"You also lied about Eric. You said he cares about body language, when he really needed my voice to know I saved him from the storm, that's why you wanted my voice, and why you posed as a brunette with my voice." Ariel interrupst, pointing out another fact.
Ursula just smiles evilly, and looks at Ariel.
"And you neglected to mention that the spell you are going to use should I fail to meet my bargain, also was intended to be lethal, and that you also had a hand in having them fail their end of the bargains. Would you care to explain that, "Saint"?!" Ariel shouts angrily.
Ursula relaxes a bit. then smiles in an almost conforting manner.
"Ariel, if you ever trusted me, then hear me: existance needs you. Need your life!"
Ariel now realizes completely that Ursula intends to kill her in a sacrifice, and as Ursula outstretches her arm in an attempt to grab her, Ariel back-flip-swims a few inches away.
"......!" Ariel reacts in shock and horror.
"You carry such a burden, princess... To give your own life so that existance might reset to be perfect for us... Do you not see how wonderful that is?" Ursula says in maniacal glee.
"You're mad..." Ariel responds fearfully and angrily.
Ursula continues with her mad beliefs, but doesn't mention what's in store for Triton yet (or at least, doesn't make it quite clear to Ariel).
"Now, someone else may make a more powerful sacrifice, yes, I can sense him coming... hehehehe, and I can have our desires fulfilled." Ursula gloats to herself.
She then looks at Ariel.
"You see, girl, We don't need you completely... A more powerful figure can make a suitable sacrifice for both our needs. And since you are already unwilling to comply to be a sacrifice... I'll just rip your soul from your bloody corpse!" Ursula gleefully, and maniacally, tells Ariel.
Ursula's hair starts flying erratically, as if the wind is blowing it.
"I'm not ready to die, Ursula, you still owe me answers... like this "more powerful being"." Ariel says.
"Poor unfortunate soul, if only I could make you see. now die, and YIELD [YOUR SOUL] TO ME!!" Ursula shouts.
She then teleports above Ariel. and has two neon colored potions surrounding her.
"ELECTRUS!!" Ursula chants.
Suddenly, the Potions explode, revealing an electric energy barrier, which she then tries to ram Ariel with.
"EHEHEHEHEHEHEHEHE!!!" Ursula laughs maniacally.
Her spell then cancels out. She then teleports out, though not before recieving a hit from Ariel.
she then teleports to another area, and the has several crimson potions surrounding her hand.
"Crustio" Ursula chants.
The potions explode into fireballs, and aim towards Ariel. She manages to dodge most of them, but one hits her, completely destroying her dress and ribbon. She then tries to hit Ursula, but she teleports at the last minute. She manages to hit Ursula when she reappears, though. She then tries Electrus again, Ariel manages to dodge it.
"HYAHAHAHAHAHAHAHAHAHAA!!!" Ursula cackles insanely.
Ursula then teleports again, and then attempts to use "Crustio again. This time, Ariel is able to dodge
all of the fireballs. Ursula then swoops down, and takes out an aqua-colored potion and drops it.
"GLACIAS!" Ursula chants.
portions of the Ocean floor turn to ice. Ariel only avoided it due to swimming up and pounding Ursula's head.
Ursula gets very annoyed at this.
"YOU...!!!" She begins to shout, and teleports.
She manages to hit Ursula and dodge the Crustio spell. Ursula then teleports and tries to use Glacias again, but to no avail, and she's still being pounded. She then is too angered to focus, and she teleports and then she disappears as she say's "DIE, ARIEL!!!".
Ariel then senses underwater waves coming behind her, and dodges a punch from Ursula, with Ursula saying "HOW DARE YOU..." before teleporting, and trying again in a different direction, saying this time "...EVEN FORGET..." before teleporting again and doubling back shouting "...WHO HELPED RAISE YOU..." before teleporting and trying a different direction shouting "...YOU..." before teleporting and trying for the last time to hit Ariel, finally finishing her shout with "...STUPID PRINCESS!!!" and teleports back above Ariel. She then tries to attack with Electrus yet again, but yet again fails. She then tries a very dark version of how she curses failiures of her deals, but Ariel somehow manages to absorb it and after hitting her. repel it back. resulting in Ursula shouting "WHY.... YOU... HAAAGHHH!!!!" as she sinks down.
"Darn it! I was so close.... I could... taste the power... and her... resurrection..." Ursula struggles to say.
"I don't understand, your desires would cause you to die! Why would you want to get that power?!" Ariel asks.
"Because without their souls, I'll never destroy that infernal seal. and gain the power of ruler..." Ursula Gasps.
Ariel realizes what she means.
"...Seal?! You told me and my father that you had no longer been possessed by the demon's Soul and that he banished you because of claims of treachery under your free will!"
Ursula then smiles maniacally.
"Of Course! she had started to repossess me, now it's to the extent that, even with the Heart of Darkness destroyed, she has near total control of me! I am to realize this worlds destiny, for me to be ruler of the Seas, as well as the resurrection of our evil lady of destruction, Vanessa!" Ursula gloats with maniacal glee.
"the world doesn't wish for this..." Ariel says.
"her powers come from the souls in all life, Tell me. why am I trying to resurrect her with their souls, because they are dark enough as it is, And she intends to remake this world... Haaaa ha ha ha ha ha!" Ursula laughs.
"I thought that defeating you those eight years ago would have saved you from her, but now I realize that you have been irreversibly driven mad!" Ariel says.
Ursula then gets up.
"No, Ariel... How can you be blind to this? If you refuse to see... then you are the fool!" Ursula growls.
Suddenly, Dark energy engulfs Ursula temporarily, and then she laughs maniacally.
"HWAHAHAHAHAHA!!!! OH ho ho... what's this? This Power, My strength is returning! Yes, My lady, I shall destroy this infernal seal with Ariel and Triton's souls, as well as your own blessing! ...Truly Providence, that Vanessa would honor me with her guidance!" Ursula shouts.
She then notices Ariel and lunges towards her and grabs her, and swims to the distance, with Ariel in tow, shouting "LADY VANESSA!!!"
"(No... I feel a new power.)" Ariel thinks.
She then realizes that she heard her mention her father as being a sacrifice as well.
"Wait, What Do you intend to do with my Dad?!" Ariel shouts.
Ursula swoops down.
"Poor little princess, it's not you that I'm after, but a much bigger fish..."
but before she could finish, they hear a familiar voice.
"Ursula, STOP!!!"
Daniel 
