How do you evolve your starter in Pokemon Explorers of Time?

Answer 1

In Pokemon Mystery Dungeon 2: Explorers of Time and Darkness, you must have undergone a significant part of the plot in order to evolve your starter Pokemon. This means that you must have finished all of the plot up to the point where you return from the future and foil Dusknoir's plan to eliminate you. Essentially, you will need to have defeated primal Dialga in Temporal Tower. Once you defeat primal Dialga, the guild will call for your graduation as a complete and qualified exploration team. Wigglytuff, the guild leader, will announce that you must face the 'Grand Master of All Things Bad'. This requires you to navigate Mystifying forest, which leads on to Luminous Spring. After defeating the 'Grand Master of All Things Bad', you will be allowed access to Luminous Spring to evolve your Pokemon. You will, however, encounter a difficulty when trying to evolve either of your starter Pokemon. The Spring spirit will comment on the strangeness of the space surrounding them. This is from Dialga bringing them back from oblivion. The space tear surrounding the two will prevent them from evolving. That is until you battle Palkia and recruit it. As Palkia is the ruler of space, it can mend the space tear around your starter Pokemon, allowing them to finally evolve. So, from there, simply go to Luminous Spring and select your starter to be evolved. Do note, however, that some starters may need an item to evolve (such as Pikachu, needing a Thunderstone).

Answer 2

First you have to finish the game (defeat Darkrai) and then you have to recruit Dialga and Palkia.