I do spoil the entire story below, but there's not much to it anyway.
This has got to be the best looking worst Pikachu short of all (so far). Comparing this Pikachu short to the others really puts in perspective how far Pokémon had come in terms of animation.
Unfortunately there's not much to this Pikachu short other than that you get to see a few mythical Pokémon. If you are a huge fan of the Entei Pokémon movie you'll be delighted to know that we make a return to the unknown dimension, this time it looking a lot more fun that portrayed earlier. However, the story is not very interesting, they help get back a lost unknown, for some reason they meet Mesprit Azelf and Uxie and Deoxis before playing around in the unknown dimension and then promptly return to play with their fellow Pokémon .
As usual they are being followed by Meowth, this episode it being 3 whole times that Marill sang and put them to sleep. I gotta admit, it got old after the 2nd this generation of Pikachu shorts.
They get plus points for featuring all Pokémon from ash and friends towards the end of the anime.
I highly recommend watching this in Japanse, Its great fun and they use very easy language in case you are wanting to start learning Japanse or have started recently. The Pikachu shorts are made for a young audience after all.
