Alternate Character Interpretation: While the English ending song, Together We'll Make A Promise, is most likely meant to be about May and Manaphy, the lyrics note such as "In our never-ending journey, the roads have split apart" could easily be interpreted to be about Ash and any of his friends that he's parted ways with. This would be especially fitting since this was the last Advanced film and thus the last where May and Max appear note Several Advanceshippers have further claimed the song as their ship's official song, both for the aforementioned reasons and the film's already prominent Ship Tease between Ash and May. .
Americans Hate Tingle: Manaphy is disliked by many American child fans (and a Base-Breaking Character for teenage and adult fans), due to it having tantrums without May so often, that it constantly comes off as whiny. But In Japan? It has beaten fan favorites like Celebi, Jirachi, Shaymin, and Victini in Pixiv's (Japan Only) Popularity Poll.
Base-Breaking Character: May and Manaphy is either seen as an adorable relationship or a rip-off of Misty and Togepi.
Contested Sequel: If this movie didn't have it hard enough as it is, it had the misfortune of following up Lucario And The Mystery of Mew, widely considered a Surprisingly Improved Sequel and among the best of the Pokemon films. To say Temple Of the Sea had pretty lofty expectations to follow is putting it very mildly.
Ensemble Darkhorse: Manaphy has only been around in one movie (and a 2014 Pikachu short), but gets a lot of fanart and YouTube videos from adult fans.
Lizabeth can count, too.
Fountain of Memes: Manaphy gets lots of memes for being called "Prince of the sea" when it's technically not an actual Prince at all.
Fridge Brilliance: More like Fridge Sadness: the movie chronologically takes place shortly after the Kanto Grand Festival, judging by its Japanese release date and the presence of Ash's Aipom. This means that May lost the festival and had to say goodbye to a Pokémon she viewed as a surrogate child all within a very short time frame. No wonder she becomes so depressed during the last stretch of Battle Frontier...
Downplayed when Max is looking at one of the water-globes with the Pokemon in them. A Gorebyss pokes out of the water and startles him. One might assume it was just saying "Hello"...until you realize that Gorebyss is a vamparitic parasitoid that sucks its victims dry and kills them. It might have been greeting him, or it was trying to feed on him. At least it was a tamed Gorebyss, which means it probably gets fed by its owners, and they're right nearby if it tried anything.
Jack Walker's backstory. He got lost in the mountains during a blizzard and a bunch of Furret and Swablu kept him warm. It's meant to be a touching tale explaining why he became a ranger, but one must ask why a child was wandering around all alone in such an environment.
Ash stuffing May, Manaphy, and Pikachu in a very small tank as he goes off to restore the power to the temple alone. There was no visible air tank on that thing and somehow the three of them taking all the air didn't suffocate them. And even if it could keep them alive, had Ash failed, they'd be stranded in deep waters in a claustrophobic tank and no one knowing their location.
In a similar note, where are Ash's Pokemon (save Pikachu and Corphish) during the entire ordeal? If Ash died during the sinking, either of the two available options could be horrible to an extent: a) if they were staying in the Blue Lagoon, then they would the next day wake up and realize their trainer is gone, or b) they were with Ash the whole time; sure Swellow, Sceptile and Aipom could have jumped out of their Pokeballs to save Ash, but how about Donphan?
Ash's Hoenn Pokémon, except Corphish, only appear for a few minutes. And it's in those few minutes that we get to see Sceptile in his only movie appearance note As a Sceptile anyway; he appeared in his Grovyle form in the previous two movies.
The Scrappy: While normally a Base-Breaking Character at worst, Ash's presence in the movie, particularly the scene where he shoves May into a pod and hijacking the climax from her in her own movie, has been derided as a one-man Spotlight-Stealing Squad from May in her own movie. That's not factoring in the Super Saiyan moment he later has. Had this been Ash's movie, this would be fine, but this was May's movie, not his.
Sequelitis: Generally considered one of the weaker Pokémon movies, due to its unoriginal plot combined with Manaphy's presence. Certain fans are more kind to it though note In particular Advanceshippers, due to the film's prominent Ship Tease between Ash & May.
Squick: Phantom heartbreakingly or enviously mentions that he wanted to hatch Manaphy with his own hands. Is this guy expecting parenthood or something?
Values Dissonance: A lot of Westerners find Ash forcefully pushing May into the escape pod, essentially stealing the climax of her own movie from her in the process, to be rather sexist.
Viewer Gender Confusion: Though its higher voice and pony tail-like antennae may make Manaphy seem like a female, its gender is never officially mentioned plus it's confirmed to be a genderless species. It's maybe leaning more towards male since it's named the "Prince of the Sea" a countless number of times.