Catharsis Factor: After the sheer cruelty and brutality the Iron-Masked Marauder has committed throughout the movie, not to mention almost causing Celebi's death, it's truly satisfying to see him fall from a great height into the forest, then see him rendered completely powerless and humbled by a bunch of Com Mons.
Complete Monster: The Voice of the Forest, by Howie Dewin: Iron Mask is an exceptionally vicious agent of Team Rocket who schemes to claim Celebi's power for himself. Introduced burning the camp of a hunter and threatening the lives of many Pokémon to extort information, Iron Mask uses his "Dark Ball" technology to corrupt Pokémon into his slaves. Later capturing and torturing Celebi into submission, Iron Mask reacts to Ash trying to save Celebi by crushing Ash's fingers under his boot until the boy faints from the pain. Iron Mask then forces Celebi to begin ravaging the very forest it has always protected, endangering the lives of hundreds of Pokémon while Iron Mask proclaims his intent to take over Team Rocket, then the whole world. When Ash and his friends stage another rescue, Iron Mask tries to force Celebi to torture and kill the children.
Ending Fatigue: The film feels like it's wrapping up when Celebi is revived by the time-travelling ones......only for Marauder to pop out one more time to try and catch it again, leading to another confrontation.
Nightmare Retardant: The twig monster Celebi was controlling. It looks creepy at first, but as it gets more screen time, it just looks ridiculous and out-of-place with its conspicuous and aged CGI. Even the bellowing sound it utters becomes awkward when it repeats the same sound time after time, making it seem like a stock sound effect.
Padding: The English version adds a sequence of Team Rocket fighting over a peach, which contributes nothing to the plot, even compared to the other scenes added.
Sequelitis: While few will say 4Ever is completely horrible, fans generally agree that it's the weakest of the original movies and pales in comparison to the first three note all of which were written by Takeshi Shudo, who wasn't involved in this movie nor any of the subsequent ones, and it's often agreed upon that this is where the movies degraded to being So Okay, It's Average at best.
Special Effects Failure: You can obviously tell that CGI was used for Celebi's twig monster, and not very good CGI at that.
Despite his darker presence and his brutal tactics, many people view the Iron Masked Marauder as an incredibly underdeveloped villain. While his goal to corrupt Celebi and use it to overthrow Giovanni would have made for an interesting villain arc, his motive for doing so is purely based on a thirst for power and a desire to Take Over the World, and there is no insight on the relationship between him and Giovanni. Furthermore, his goal to capture Celebi, the time-traveling Pokemon, becomes even more staggering when he shows no interest in using Celebi's time-traveling powers towards achieving his goal. All things considered, a lot of people agree that Grings Kodai is more like what IMM should have been.
Suicune gets an early appearance in the movie, along with a description that includes its ability to purify water, and serves as a partial motivation for Ash and his friends to explore the forest. But it doesn't arrive to help the heroes until the third act, only providing limited assistance against the villain and a brainwashed Celebi, and while it does purify the lake, it's not enough to save the dying Celebi, requiring another Deus ex Machina from the other time-travelling Celebis to do so. Ultimately, as cool and majestic as it is, it's contributions overall feel rather negligible.
As Suedepointed out in his review of the movie, Celebi's death could've been used as an effective Green Aesop - if Celebi stayed dead, it would give the message that sometimes damage done to the environment can never truly be undone.
The movie itself also caused an example to occur within the main series: the GS Ball storylinenote which had been running for over 60 episodes and was the whole reason Ash and friends went to both the Orange Islands and Johto in the first place was meant to conclude with The Reveal that the GS Ball contained Celebi, in turn leading into a multi-episode story arc. When it was decided that Celebi would be featured in this movie, the writers shelved this and the GS Ball storyline went unresolved to this day.
The Woobie: Considering their usual depiction of evil, unstoppable juggernauts, the Tyranitar that gets caught by the Iron-Masked Marauder is this. When it first appears, it's so scared one just wants to give it a comforting hug. And it only gets worse for it afterwards.
Writer Cop Out: Some people might see the emergence of dozens of time-traveling Celebi to revive the main Celebi as this, especially since the film, for some reason, faked the audience out once with a previous Deus ex Machina that turned out to not do any good.
of the movie, Celebi's death could've been used as an effective Green Aesop - if Celebi stayed dead, it would give the message that sometimes damage done to the environment can never truly be undone.