This movie didn't have an animated short, just to let you'll know. So let's start!
Actual Movie
The film focuses on Celebi who travels to the future with a boy named Sam when being chased by a hunter. Ash, Misty, Brock, and Pikachu are on their way to the next gym in their Johto journey and get a lift from a man named Maki who takes them to his hometown of Arborville. They see a Suicune (who was actually the first Pok?on Ash saw in Johto). When they plan to enter a forest that is claimed to have many unusual and rare Pok?on, they are warned by an elderly lady about the "Voice of the Forest" which may carry a person off to a different period in time unless those hearing it stand still.
Ash and the group encounter the Voice of the Forest and find Sam in the forest, but Celebi has already fled. Sam awakens and discovers he is 40 years in the future from when he was. He, Ash, and the others search for Celebi and they find it in a tree. After some convincing, the gang manage to gain Celebi's trust. They run into a member of Team Rocket, the Iron Masked Marauder, who is trying to capture Celebi. Jessie and James also team up with the Iron Masked Marauder to capture Celebi. The heroes take Celebi to its home, the Lake of Life, where it is healed by the water. The group spend the night in the forest. The next day, Celebi is captured and is turned evil by a special type of ball, the Dark Ball, a ball with special powers that will enhance the captured Pok?on's powers and turn it evil, that the Iron Masked Marauder used. The Iron Masked Marauder orders Celebi create a giant dragon shape made from parts of the forest. The heroes, and Meowth and James (Jessie was spun into the giant dragon creature and trapped), chase after Celebi in Maki's flying boat, but are brought down by the evil Celebi's attacks. The Iron Masked Marauder tries to kill Ash and Sam, but Suicune saves them. Onix and Suicune do battle with the Masked Marauder's evil Tyranitar, while Ash, Sam, and Pikachu clamber into the dragon shape and manage to get Celebi to remember its memories, successfully bringing Celebi back to normal. With the destruction of the dragon shape, Jessie and the Iron Masked Marauder fall into the lake. The other heroes rush to the lake's edge and find Ash and Sam with Celebi, who suddenly falls limp. Ash and Sam realize Celebi is dead and everyone weeps. However, the Voice of the Forest materializes in the sky and thousands of Celebi appear and resurrect Celebi. The Iron Masked Marauder appears and kidnaps Celebi and flies up with a jetpack, but Ash and Pikachu hold onto him as he flies away. Pikachu destroys the Masked Marauder's jetpack and they fall to Earth, but Celebi saves them. The Iron Masked Marauder falls down to the forest floor and is confronted by the old woman, her granddaughter Diana, and Maki. Celebi prepares to bring Sam back in time. He has an emotional farewell with Ash and departs. Later on, Ash and friends are talking with Professor Oak who tells Ash that he and Sam will be friends forever. After the call is ended, Misty wonders how Oak knew Sam's name, since they never told him. Oak is then reflecting on the event, saying it seemed like only yesterday.
Note from Me!
For those of you who don't get it, I'm going to tell you, but first i must explain what happens when the credits roll, and in that short summary will be the secret! he credits end with Tracey clearing Oak's room and finds Sam's drawing pad, containing a faded sketch of Pikachu and Celebi. The reason being that Sam was actually a young version of Professor Oak, whose first name was Samuel.