- Base-Breaking Character: Alva is seen as a Flat Character who, like many Pokémon movie villains before him, has no backstory, personality, or motive beyond greed. Then there are those who would look past this because of his "forced Mega Evolution" gimmick.
- Broken Base: The device that connects Ash to Volcanion has been contended, mainly because Ash wears it over any outfit he's in such as his regular clothes, his detective-inspired clothes, and even his underwear. Some are okay with this while others think this is a way for the anime to talk down to its viewers, thinking they won't be able to remember Ash is connected to Volcanion.
- Cliché Storm: The plot revolves around yet another cardboard villain trying to use a Legendary Pokémon for his own ends, something done by almost half the other movies.
- Complete Monster: Cabinet Minister Alva is a cruel, scheming man who seeks to usurp control of the Azoth Kingdom through force. Alva devised a technique known as the Mega Wave, forcefully and painfully trapping Pokémon in their Mega Forms, including his own Gengar, using them in his attempt to take the power of Magearna. Alva assures Magearna's compliance by torturing Ash and his friends, before tearing out Magearna's mechanical heart, forcing Racel to watch. Using Magearna's heart to empower his flying fortress, Alva attacks the Nebel Plateau, forcing Magearna to ravage its own home, and spitefully tries to destroy the plateau and everything on it by letting his fortress plunge into it. It really speaks volumes about Alva's depravity when Alva's Gengar flees upon being freed from his control, something not even Grings Kodai's Pokemon did.
- Fridge Brilliance: It's possibly enforced that Volcanion is the more active star while Magearna doesn't fight as much: Volcanion is the third Mythical Pokémon of Gen VI, not Magearna (who is instead in the first Mythical Pokémon of Gen VII), so it's going to be the one showcasing its power to attract people into having it. Though this crosses back into Fridge Logic when you wonder why anyone — especially Pokémon — would want to undersell the hot then-new powerful Pokémon from the next set of games.
- Fridge Logic: Given Alva's goal is taking over the Azoth Kingdom, and how he has an army of simultaneous and powerful Mega Evolutions under his command, one must wonder why he even needs Magearna at all, and doesn't just use what he already has to hold the kingdom hostage.
- Harsher in Hindsight: Alva's forced Mega Evolution gimmick becomes this in light of Generation VII's Pokédex entries also characterizing Mega Evolution as a Superpowered Evil Side, with many Pokédex entries noting that the Pokémon are suffering from using Mega Evolution. Some entries go as far as to describe the Mega Evolved Pokémon as victims of full-on Body Horror. Couple this with the fact that Alva's Mega Wave not only unnaturally induces Mega Evolution but also compels the affected Pokémon to do his bidding and it's little wonder that even Alva's own Gengar would quickly abandon him once free from his control.
- Hilarious in Hindsight: The title including the words "Mechanical Marvel" should amuse those aware of Pokémon Live!. Magearna's status as an artificial Pokemon made by humans as a weapon also brings the musical to mind.
- "Holy Shit!" Quotient:
- When the heroes have to rescue Magearna's Soul-Heart, they have to fight again fourteen Mega Evolved Pokémon at once!
- During the climax, the residents of the Nebel Plateau establish themselves as one of the gutsiest groups of supporting Pokémon in series history, banding together to engage in a team Beam-O-War against Alva's Soul-Heart-fueled laser cannon. And just when it looks like these Ridiculously Cute Critters are about to go the way of the dodo, Squishy transforms into its Complete Forme to join in.
- It's the Same, Now It Sucks!: The movie's most noted flaw is that it follows a pattern almost half the other movies follow. It does have a few things that set it apart, but not enough to be really unique or groundbreaking.
- Just Here for Godzilla: Even some of those generally uninterested in the movie have considered watching it for the battle between the Kalos gang and the Mega Evolution army, and Zygarde's Complete Forme. Or even for the end teaser, featuring the first animated appearance of the Alola starters.
- Like You Would Really Do It: Death is rarely a permanent affair in the Pokémon films and specials, with only two major exceptions by the time Volcanion and the Mechanical Marvel was released: Latios and Lucario. (If one were to count Entei and Mirage Mew, that puts the total up to a meager four.) Beyond that, Magearna had entered a state of near-catatonia due to the physical and emotional trauma it suffered at the hands of Alva, and had only just started to recover from it upon seeing Volcanion; turning Volcanion's Disney Death into a major Yank the Dog's Chain moment would've likely made for an even more Bittersweet Ending than what Heroes had. With this in mind, Volcanion's miraculous survival was not entirely unexpected.
- One-Scene Wonder: Squishy's Complete Forme appears for a couple of seconds to aid the good guys.
- So Okay, It's Average: It has its pros and cons and is seen as the better of the two controversial XY movies (and a fairly decent one in and of itself, as the last movie didn't set particularly high bars), but not quite up the lane of Pokémon movies like Pokémon Heroes or Lucario and the Mystery of Mew.
- Surprisingly Improved Sequel: Despite the So Okay, It's Average reaction, this movie is considered a vast improvement over its predecessor.
- Tainted by the Preview:
- Inverted to some extent, as most of the early interviews and reviews actually put the movie in a more positive light, compared to the past two XY movies. The fact that most voice actors were visibly enthusiastic about their work on the movie and its music sure helped. Of course, there were those who saw it as the typical hype-spinning of the PR Machine in motion.
- However, it was tainted in a different manner. One hyped-up scene the previews promoted was the debut of Complete Forme Zygarde being shown on the big screen. Normally, it would have been the main draw of the film for fans not interested in the movie, but Complete Forme Zygarde was already advertised to be featured in the XY&Z's Team Flare arc, with a more plot-relevant reason to be there than the movie provides. Combined with a more dramatic storyline that was building up since Team Flare's debut and this movie's lack of connection with the story arc, most found it best to simply wait for the Team Flare climax instead in order to enjoy Complete Forme Zygarde in its full glory.
- They Wasted a Perfectly Good Character:
- Magearna's power is said to be able to change the world, but despite this, Magearna itself doesn't show it. It rarely, if ever, fights opponents, and once Jarvis takes the Soul-Heart, it spends the rest of the movie on the sidelines.
- Alva has an interesting ability to mass-Mega Evolve Pokémon, and his scientific skills and high status ought to have made him an interesting character. Instead, no backstory is provided for him, he has no real motivation beyond greed, and he comes off as one of the blander Lawrence III expies.
- Writer Cop Out: The drama, gravity and tension of Volcanion's Heroic Sacrifice (even described by Ash as a suicide mission) are lessened considerably when it simply shows up alive and well.
YMMV / Pokémon: Volcanion and the Mechanical Marvel