Mysterious Grotto is an area in Project: Pokémon and can be accessed by talking to the NPC in Celadon City's PokéCenter. You can find many different types of Pokémon as well as a Mythical Pokémon.
For a limited time, Groudon, Rayquaza, and/or Kyogre can be changed to a new aura for 64 BP.
Deoxys, the Mythical Pokémon, can be found in one of the Pichu patches with Solrock and Lunatone which can both be found in Victory Road. If you don't have Solrock and Lunatone, Deoxys will not appear.
Changing Deoxys Forms
Deoxys has multiple forms that it can transform into: Attack Deoxys, Defense Deoxys, Speed Deoxys, and Normal Deoxys. You can change its form by finding meteorites scattered around the area. A text will appear describing the meteorite to hint at what form Deoxys would change into.
The Battle Tower found in Mysterious Grotto allows you to battle 5 NPC trainers in a row with 3 of your Pokémon. For each round, your Pokémon will be healed to full HP. Some Pokémon may be banned from entering battles and item usage is prohibited. If you participate in the Battle Tower, you will have to defeat 5 trainers to get BP or Battle Points. Battle Points can be exchanged for a variety of prizes that can be bought upstairs. Behind the Battle Tower is an entrance that leads to a red NPC. All of their pokemon are level 100.
|Pichu||In Pichu nests|
|Anorith||In the cave|
|Armaldo||In the cave|
|Baltoy||In the cave|
|Houndour||In the cave|
|Spoink||In the cave|
|Torkoal||In the cave|
|Deoxys||In the Pichu patch with Solrock and Lunatone|