Mew appears tantalizingly at the begining of the first Pocket Monsters film. At the time of the movie's release, the Mew characters was still very mysterious. Only available at the end of the game and unlisted on capture lists, the just-out-of-sight creature teased viewers just as much as it did the titular character. we know that Mew is mysterious and legendery, and we know it is the most sought-after Pokemon, theoretically the "missing link" Of evolution (no, not the Missingno). As the story continues, we see it is not only rare, but seemingly playful and lighthearted. This aspect becomes confused towards the finale: the giddy and childish creature displays personality traits that are...well...incongruent.
Mew’s personality is bubbly and child-like, although it seems to have a very mischievous streak, teasing all it encounters by staying just out of sight. Mew spends most of the movie playing, elicting "aawww!" noises from female audience members as it bounces on bubbles, chases windmills and plays follow-the-leader with Team Rocket. We assume that Mewtwo's anger towards it's genetic parent is misguided -- how could anyone be angry with such a sweet little creature? But when push comes to shove, Mew acts decisively and with an authority that does not fit with it's playful image.
Mew follows Rocketto Dan into the corridors of the castle as an extention of it's game, but in Mewtwo's laboratory it stops playing and starts watching. The Pokémon gamebooks state that Mew is known to have a long-term memory, and in that way can learn and judge. Long term memory usually accompanies perception of the future, and symbolises a sentient mind. (meaning Mew is self-aware and can think) So, has Mew been "playing dumb" to gain entry and better asess the situation? It would seem so.
Mew does not act until it is necessary --to rescue Satoshi, who has proved himself worthy through his demonstrations of compassion (although Mew does display a similar sadistic streak to Mewtwo when it pops the bubble Satoshi is sitting on and lets him drop to the stone below and bruise his tailbone).However, Mew is careful to maintain the sweetness and light personna, by playing on the bubble used to save the boy s if it were simple coincidence that he was saved. However, Mew has still made the first move. Mewtwo attacks first, but Mew has already set the fight in motion by interfering with what it had previously ignored.
In a case of foreshadowing and insight into Mewtwo's motiations, Sakaki makes a comment on the CD Drama that a clone can prove it's worth by defeating all around it. Mewtwo can defeat any wild Pokemon and any trained one, but longs to truly know it's own potential. Sakaki elaborates that, with enough power and noteriety, Mewtwo willal most certainly attract the attention of Mew, if it exists. Here Mew is, but it ignores him. Mewtwo's pride is wounded.
The feline original continues to play the part of the angelic animal up until the point where Mewtwo finally lands a blow. Mew does not like being struck, and Mew strikes back. The fight begins in earnest as the two buffet each other with explosive energy blasts. Finding themselves evenly matched they come to rest on opposing sides of the stadium, hovering symbolically over the two camps --original and clone. Mewtwo observes the ineffectiveness of their fight, but assertes that the clones have been created stronger than their genetic ancestors. Mew then plays the pride card -- It responds that the original is the only real monster, and that in battle, as in life, the original will win out. Mewtwo is incensced by this insult and the battle resumes.
Mew is a decepetive character. For all the soft colours and wide eyes, a calculating mind is present. Mewtwo and Mew are often contrasted, but in this case a comparison is more than warrented. Once the fight is on, Mew and Mewtwo need not be differentiated between. Both are blind to everything around them as they try to tear each other apart. Neither exercise restraint or display concern for those in the path of their fight.
Mew reverts to a kittenish state when Satoshi is caught in the crossfire of their private war. As the boy's body drops to the ground, Mewtwo is shocked enough to stop fighting, but Mew only cocks its head to one side. Mew seems not to care that a life has been lost due to their battle, even though it is a life Mew saved not an hour ago! This coldness may not be intentional. Mew is said to be, if not omnipotent, near immortal. Therefore, it's understanding of death would be narrow. Comparing this scene to CD drama, Birth of Mewtwo, we see the child Mewtwo react similarly when Ai passes away. Too young and inexperienced to comprehend the meaning of death, Mewtwo instead feels abandoned. Mewtwo cried for his companion. In Satoshi's sacrifice, They are the only two not to shed a tear. However, the matter has been settled over the trainer's sacrifice. Neither Mew nor Mewtwo have any desire to continue thier fight after realizing the fragility of the lives they are playing with and the weightiness of their own powers. They concede that by mere merit of existing they have proven they have strength. They are too evently matched for one to ever conquer the other. Mew and Mewtwo confer and decide it would be best if the incident were, literally, forgotten...
In this context, Mew is just as guilty as Mewtwo is in both the battle and the death of Satoshi. Neither have a hand in his ressurection. Mewtwo's motivations are based in his childhood and experience with the human world. Mew's are unclear. From the CD Drama, we know that Mew was involved in Miyamoto's diappearance, and from Myutsuu no Tanjou we also know that Mew had knowledge of the Mewtwo experiment. Why did it choose not to intervene earlier on? Why does it choose to reveal itself to the Rocket Gang after centuries of approaching only the native people of the Andes region? Mew is a phantom pokemon, and Mew is a mystery. Sometimes things stay that way.