Morgana is as cruel as her own sister. She shows that she hates being criticized in the movie when she berates Undertow. Morgana is deceitful, baleful, and ruthless. She wants to steal the trident to prove her superiority over her sister. She lacks her sister, Ursula's deviousness. She also is not as good as using potions as her sister was as shown when Morgana fails all attempts to turn Undertow back into a shark. Morgana is shown to have funny, though, malicious sense of humor, such as at the beginning when she grabbed Eric's advisor, Grimsby and said "Now, is that fair Gramps, I asked you". She tickled Grimsby chin with her fingers and with a nice smile. She then said "But then, whoever said we had to play fair?" Though Morgana's personality differs she does have the same objective as Ursula. Many people think she was a less interesting Ursula. At the same time, however, she was much more cunning than Ursula, and managed to hang on to the trident longer than her. Although she ultimately desired vengeance against Ariel and Eric for their role in Ursula's death, she, also at the same time hated her due to her neglect from her mother, as the latter favored Ursula far more.
Morgana appears very thin, closer to a squid than an octopus. She is younger than her sister, and her skin and octopus arms are green, instead of purple like Ursula's.
When Morgana was young, she was liked less than Ursula by her mother. She also knows less magic than Ursula does. Morgana received frequent criticism for her jealousy of Ursula. Their mother soon died as revealed by Morgana when she, herself, unsurped King Triton's throne, becoming queen herself. A picture of Ursula and Morgana's mother was seen in the deleted scene "Gonna Get My Wish". It is less likely she was banished from King Triton's kingdom like her sister Ursula was though.
The Party celebrating baby Melody's birth is interrupted by Ursula's vengeful sister Morgana attempting to prove her superiority over Ursula. She attempts to feed Melody to her shark, Undertow, but fails when Undertow is changed into a piranha and Prince Eric and Ariel rescue Melody. So, Morgana, Undertow, and her two manta rays, Cloak and Dagger leave inside a huge funnel. While Morgana leaves, she threatens to return and have her revenge on everyone, mainly Melody.
Morgana, Undertow, Cloak, and Dagger now live in an iceberg lair. Morgana is now trying several attempts to change Undertow back into a shark but all fail. Morgana now believes that it is no use getting the trident and that trident is too powerful for her to overcome. It is soon revealed that Morgana does not like being criticized because all her mother ever did was criticize her and tell her she should be more like Ursula. It is also revealed that their mother favored Ursula more than Morgana. Morgana and Undertow argue about whose fault was what about hiding in the lair. The orb light shines and Morgana goes and sees Melody's hands holding the locket. They both get an idea. They decide they will use Melody as the tool to Triton's undoing.
Morgana sees that her time has finally arrived when she sees Sebastian's failing attempts to stop Melody from going out to sea to find out the secret of the locket. So, she sends Undertow, Cloak and Dagger to lure Melody to her lair. The plan succeeds.
Morgana welcomes Melody to her palace, offering repellent culinary, and reveals the secret of the locket. She then, transforms Melody into a mermaid with Ursula's last magic potion that Morgana's been saving for a special occasion. After Melody's rejoicing has gone away, Undertow is angry that she didn't use the potion to change him back. Morgana sternly tells Undertow to "keep his scales on" and that she's still reeling her in. This is where she broke out in song "I'm Gonna Get My Wish Tonight!"
Melody arrives back to Morgana's lair to thank her. After Melody thanks her, Morgana sets the rest of her plan in motion by falsely crying. Morgana reveals that the mermaid spell is temporary. Morgana lies to Melody that "her" trident was "stolen" by a "deranged kleptomaniac" (she's referring to King Triton and his trident) and that "there is no one left to give it back for her". Melody tells Morgana that maybe she could get it back for her. Morgana acts surprised. She shows Melody the map and where the "scoundrel" lives. Melody asks if she means that it wasn't just "an ordinary fish tale" like her mother told her and if it really exists. Morgana says "Of course it exists. Whoever told you otherwise?" Melody tells Morgana that her mother did. Morgana responds that she's sure Melody's mother didn't mean to be cruel and deceitful. Melody says that she will bring back 'her' trident, and that she can count on her. Morgana says, "Be careful, dear! Enjoy those fins!" Then she says softly with an evil grin "while you can", and chuckles sinisterly.
Morgana sees Melody, Tip and Dash near Atlantica. Morgana sends Cloak and Dagger to go and make sure nothing interferes with Melody's return.
Ariel and Flounder have followed Cloak and Dagger to her lair. Just as Melody is about to give Morgana the trident, Ariel shows up and stops her, frantically. Melody is angry and shocked that Ariel hid the truth about her locket. Morgana and Ariel are trying to convince Melody to give the trident to each other. But Melody, angry at Ariel for hiding the truth about her locket, gives its to Morgana. Morgana cackles and claims that all the seven seas are at her command. She wraps Ariel up with her tentacle. Melody tries to stop her but Morgana stops her by pointing the trident at her. Morgana reveals that Ariel was only trying to protect her from her. Morgana confesses that she herself tricked Melody into giving the trident to her and that King Triton is really the king and is Melody's grandfather. Melody realizes the truth. Morgana blames Melody for the theft after the girl expresses her anger over the deception stating she brought this upon her herself through her pursuit of her personal desires. Then, she imprisons Melody and Flounder into a part of her lair. She tells Melody that her time as a mermaid has just expired. Morgana then heads to the surface with a struggling Ariel in her tentacles.
Morgana rises to the roof of her own lair on top of her new cliff. Prince Eric, his crew, and Scuttle arrive to battle the now-powerful sea witch. However, Morgana destroys Prince Eric's boat. Prince Eric and his crew are forced to stand on the ice and they survive. King Triton, his guards, and Sebastian arrive to battle the now-powerful sea witch as well. Morgana dares King Triton to hurt her mocking his threats and then cackles. After Undertow taunts Triton, Sebastian chases Undertow, angrily but Morgana transforms Undertow into a gigantic shark and Sebastian manages to flees. Prince Eric takes his sword out and asks, angrily, where's Melody and what has she done with her. Morgana replies "Oh, you wanna join your daughter? Well, I think that can be arranged" She commands Cloak and Dagger to take Prince Eric to Melody underwater to drown. Scuttle distracts Morgana and Ariel is freed and she and Sebastian rescue Prince Eric, while Tip and Dash defeat Undertow and rescue Melody. Sebastian defeats Cloak and Dagger.
Morgana forces all the creatures she sees to bow down to her. Melody realizes that she has to get the trident herself since Ariel, Tip and Dash are forced to bow down to Morgana, and Prince Eric has been rendered unconcious. Melody realizes that she has legs and that power of Morgana cannot harm her. Morgana then forces King Triton to bow down. Morgana looks up at the sky and says to her mother that she has finally won. As Morgana sentences King Triton to oblivion, Melody surprises Morgana by snatching the trident from her. Morgana, eventually tries to take the trident away by tying up one of Melody's feet, she lifts Melody upside down and tries to grab the trident back, but Melody pierces the trident through one of her tentacles, distracting her. and Melody is free. Melody gives the trident back to Triton.
Morgana pushes Melody off the cliff after she throws the trident to Triton, but Dash saves Melody. Triton grabs his trident, says to Morgana, "Never will you or yours threaten my family again. There will be no escape for you! Ever!" and imprisons Morgana in a small iceberg and she sinks. Still alive while she sinks, she whimpers "Mommy!" because she realizes that she has failed her mother by being defeated. The picture of Ursula sinks along with her, a little far behind.
- The name "Morgana" is a variant of Welsh-Old English name "Morgan". It means "circling sea or great brightness", "bright or white sea dweller".
- Morgana shares her name with a character from Winx Club, Morgana.
- Morgana is very similar to Maleficent in the sense of being able to use Magic, interrupting the birth ceremony of the film's main protagonist, and then disappearing shortly afterward.
- Ironically, Morgana's voice actress is Pat Carroll, who also voiced the character's more famous sister Ursula.
- She also appears to resemble Cruella De Vil.
- Like Ursula, Morgana also appears to have a skeleton despite having an octopus (which in real life doesn't have bones) lower body. However, since she doesn't die unlike her sister (she is instead defeated by being frozen alive inside a huge block of ice by King Triton and being tossed back underwater while still conscious), her skeleton appears when she is electrocuted by the trident shortly after grabbing it, but is not harmed.
- Unlike Ursula, who has six tentacles despite being half-octopus, Morgana actually has the correct number of eight tentacles. However, based on her slender appearance and the fact that if you include her arms, then that actually makes her look more like a squid, which in real life has ten limbs like her.
- Her ability regarding her forcing the sea creatures to bow down to her resembled the ability Heartless Angel from the Final Fantasy series.
- In the game Disney Trivia 2: The Sequel, it says that Morgana has a polar bear guarding her iceberg lair, which, for reasons unknown, is not shown in the film.
- The way Triton and Sebastian react when she first appears implies they were fully aware of Morgana's existence the whole time, but did not consider her a threat probably because of her quite poor magic skills in comparison to her more powerful sister.