The very first one in the whole movie and Ariel's Establishing Character Moment would probably be the shark scene in the beginning. Seeing Ariel outwitting a shark like that is badass and pretty much solidifies her as the first Disney Princess to be an Action Girl.
Eric does a LOT of stuff that no reasonable person would do, and comes off as a major badass because of it.
The final battle, especially Eric who shows off how totally badass he is. His dispatchment of Ursuladefinitely qualifies.
Eric returning to a flaming, sinking ship to save his dog Max. And when he's trapped trying to escape, he throws him free, showing himself willing to make a Heroic Sacrifice for him.
Hell, Eric has a ton of them over the course of the movie. He's basically a prototype version of Aladdin.
Eric is brave enough to destroy a freaking gargantuan human/cephalopod monster by stabbing it in its chest with a floating shipwreck's splintered bow. You should never mess with him or his girl.
Not to mention his opening move in the fight is to dive underwater and throw a harpoon at Ursula as she threatens Ariel with her new trident.
Scuttle, after being little more than the comic relief for the entire movie, is the first one to discover that Vanessa is actually Ursula and is told and quickly attempts to stop the wedding between Vanessa and Eric. Let's just say — it does not end well for Ursula in the slightest as Scuttle recruits the entirety of the ocean to rescue Ariel. It works.
Scuttle breaking the shell pendant; Vanessa/Ursula starts strangling him for squawking in her face, but he struggles with her and gets his beak on it. Note that Scuttle was never told that the pendant held Ariel's voice, so he must have figured it out on his own. Then when she loses her grip on him, he manages to toss and shatter the shell, returning Ariel's voice to her.
In that same scene, Eric's dog Max gets a Moment of Awesome (and some well deserved revenge, since Vanessa kicked him earlier) by saving Scuttle from being strangled by Vanessa/Ursula by biting her in the butt, causing her to lose her grip on Scuttle and break the shell.
Keep in mind that Scuttle also exposed Ursula's plan in the first place, and destroyed the amulet to give back Ariel's voice and free Eric from her spell (allowing his own Awesome moment in defeating her). Beforehand, Ariel was all set to accept the same fate as her novel counterpart in heartbreak, convinced she had lost fairly but Scuttle set off all the cogs in exposing and destroying Ursula's plan.
As noted on the Headscratchers page, Scuttle could have worked out that the necklace was the source of the magic just through common sense; he may have seen human women dressed up before and guessed that it was more normal for them to wear jewels instead of a shell, giving a good indicator that's what Ursula was using (and the fact that she was using Ariel's voice, so something worn closer to her throat would make sense).
Ariel rescuing Eric from drowning. Granted, he did save her in the end (albeit after Ursula became a giant and by extension way out of her league), but Ariel is the first Disney Princess to rescue her love interest.
Related to that, do you realize how strong she must be? She's a little slip of a girl, yet is able to grab him, then pull him up to the surface and to shore with one arm, propelling herself with the other. Apparently, that collection of hers includes barbells.
Going into that, think about all the physical feats Ariel does throughout the film when she's a Mermaid; she's able to push the door to her grotto (Which is a heavy rock at the bottom of the ocean, so the pressure is there), is able to scale ships without the use of legs (Thus all upper body strength) and is able to pull against the much heavier Ursula. She's a lot stronger than she lets on for a skinny kid.
Human Ariel is no pushover when it comes to impressive athletic feats as well. While she is flailing around and drowning when she first becomes human because she doesn't how to swim with legs, as soon as Sebastian grabs her arm and points her in the right direction and Flounder swims under her armpit giving her something large and buoyant to hold on to, Ariel starts instinctively kicking her legs so fast that she swims from Ursula's lair, which is in a volcanic deep sea trench to the surface of the ocean in about nine seconds. NINE. SECONDS. When you look at the expression of focus and sheer terror on Ariel's face as she's almost at the surface, that tells you that even in the most shocking and panic filled life or death scenario, Ariel's physical strength and resolve will do what it takes to make sure she does not fail.
For even more perspective, when comparing this to the scene right before the final battle where Ariel is a mermaid again and she swims up to the surface from deep water right after Flotsam and Jetsam's death, it also takes about nine seconds. And this is compared to when Ariel is surprised and in pain from the transformation and drowning with no skill in swimming with human legs whatsoever, powered only by instinct, adrenaline, and a small push from Flounder and Sebastian. This implies that if Ariel actually practiced and learned how to swim with human legs, while she could never be underwater for too long since she can't breathe, she could be just as great of a swimmer as she was as a mermaid, or possibly even better.
It becomes a Chekhov's Skill when Flounder ferries her over to the wedding ship to get to Eric. Despite wearing a waterlogged dress and being unable to swim in her new body, Ariel clings onto the ship and starts climbing, making it in time to get her voice back.
Even more impressive, Ariel saves Eric's life again during the climax. Ursula points the trident at Eric and tells Ariel to "say goodbye to [her] sweetheart!" Quickly, Ariel grabs Ursula, changing the trident's aim so that the blast misses Eric for Flotsam and Jetsam.
Ursula is quite possibly the only villain to put together a plan and have it work completely, in part due to the Unspoken Plan Guarantee. She suckered Ariel, traded her for Triton and took over the entire ocean. The only reason she loses is because she had the unfortunate luck of running into Eric.
The scene where Ariel is naked from the seashells down after her transformation is about as awesome as it gets. Bonus meta points for the team being able to sneak that in.
Ursula's transformation from the beautiful Vanessa to the monstrous sea-witch. Ariel is finally about to kiss Eric, when the sun sets, and she becomes a mermaid again. Ursula cries "YOU'RE TOO LATE!" in a powerful, triumphant tone. She raises her arms and brings lightning down (from an ominous red sky) as she grows back into her true form, bursting through the wedding dress as her tentacles spill out in a combination of Squick and pure awesome, all while giving yet another impressive Evil Laugh. The wedding guests are understandably terrified. And this is all set to an epic, marchlike Dark Reprise of "Poor Unfortunate Souls." It's brief, but truly amazing. See for yourself.
Any time Triton uses his trident usually becomes a CMOA.
In that scene, right before Triton goes ballistic, we see that Ariel refuses to be intimidated by his Fantastic Racism. She rightfully defends her saving of Eric, saying he would have died and calls Triton on his racism by saying "you don't even know him!"
YMMV but she also doesn't let Sebastian forget that the whole mess is his fault, and he'd have saved everyone a lot of trouble if he'd kept his mouth shut.
The level of attention the animators gave to Ariel's hair. Even 30 years later, it still holds up well.
Not just her hair, but closely watch her facial expressions and body language while she's mute. The animators paid so much attention that they made her just as, if not more, expressive than she is when she has her voice.
Ariel herself is awesome as she is the first Disney Princess that actually did something and showed determination to make her dream come true.
Driven home by Ursula's little remark after the "Kiss The Girl" song. Maybe "little tramp" isn't quite the appropriate term, but can we all agree Ariel's having Eric ready to give her true love's kiss after two whole days was awesome?
As scary as it was, the way Ursula transforms into a gigantic version of herself is pretty awesome by itself. Her Family-Unfriendly Death too.
Triton threatening Ursula with the trident once she captures his daughter... unfortunately, she actually wanted him to show up.
Still, judging by what Triton does to Ariel's grotto, as well as Morgana in the sequel, if she had pissed him off enough, imagine what he could do to Ursula.
Sebastian and Flounder taking on Flotsam and Jetsam to save Eric certainly counts.
Sebastian's musical conducting; he may be smug and self-centered, but he is good at mobilizing random animals to sing for him. It finally becomes useful when he drowns out Scuttle's attempt at a dusk serenade into a soothing love song to convince Eric to kiss Ariel while he's rowing her through a lagoon. When Eric admits that he's uncomfortable not knowing Ariel's name, Sebastian quickly whispers it into his ear and ushers in a new verse of "Kiss the Girl" to get Eric to deliver the kiss.
Sebastian redeems himself multiple times - most notably organizing the plan to bust Ursula. He realizes it'll take Ariel and Flounder a while to get to the ship, so he gets Scuttle to sabotage the wedding. And knowing that they're dealing with a powerful sea witch, he goes to get Triton, having the sense to realize how far in over their heads they are. The last one is notable because when Ariel is first turned into a human, Sebastian is worried about Triton finding out and punishing him.
Ursula's Villain Has a Point moment to Ariel; as Ariel considers the deal, she points out that if she's human, she'll never see her father or sisters again. "But, you'll have your man. Life's full of tough choices, isn't it?" Ursula is absolutely right.
Pat Carroll clearly had an absolute blast as Ursula - especially in "Poor Unfortunate Souls". Hell, she was falling well and truly off the deep end of all sanity. Don't forget... she had nothing but a microphone in front of her and managed to sound absolutely 'insane;. No wonder this woman loves to come back and portray Ursula. Even to this day we're not sure if Pat Carroll was on something at the time or whether she actually is just that insane. If she was on something we want whatever that something was; if she was/is insane, we are not getting her help as it's perfect.
According to the commentary of Fantasia 2000, the people at Disney were worried about how the people of Denmark would receive the changed ending, even warning Queen Margrethe II about it beforehand. Her response to the new ending was along the lines of "He never knew how to write an ending anyways."
Decades later, at a Q&A with Jodi Benson, one of the fans asked her if she could still sing Ariel's aria from when Ursula is using her voice. Cue Jodi doing just that on the spot, and it sounding just as beautiful as it did in 1989.
The "In Harmony" number from "The Evil Manta." Ariel defeats the Manta's plans and drives him away... with one song.
Especially awesome when you remember that singing is Ariel's most noteworthy talent.
In the episode "Thingamajigger", the Evil Manta gets his hands on the eponymous item (actually a boot someone dropped into the sea) so he can threaten King Triton with it. (At the moment the boot was found, a stray cannonball from ships fighting on the surface fell and destroyed the rocks the boot happened to be pointing at - so they assumed the boot did it) Ariel, however, manages to scare him away by pointing two "Thingamajiggers" at him like a pairof guns.
What's even better about it is that the "Thingamajiggers" Ariel pointed at Manta belonged to her future husband Eric.
In "Whale of a Tale", Ariel adopts a baby killer whale, Spot, who got lost by his family. And he is too innocent, scared and childish to go back to the wild ocean. However, when three sharks attack Ariel, who has been like a mother to him, Spot gets mad. And the way he beats the crap out these terrifying sharks, is just... beautiful.
The music in this episode is so good it makes all the others look lame.
Scuttle's Pep-Talk Song to Ariel when she collapses from her attempt at walking. He rallies all the birds to motivate her, and soon she's dancing with them.
Whereas Eric saves the day, it's quite different in the stage/Broadway musical. Without her magic shell that she was given by her father, Poseidon, Ursula will die without it. In the climax, Ariel smashes the shell, destroying Ursula and saving the day.