There are a total of 12 rookie digimon. You start out with seven and need to unlock five along the adventure.
All rookie and Mega digimon do basically the same damage and have no special attributes to them so I will just list them. They do have different attacks but do basically the same damage for releasing D-Spheres.
Note: All digimon with a ~ next to them means that they have to be unlocked.
Note 2: The digimon in the rookie column have there Mega listed in the same order. Example: Renamon is #3 in the rookie column and Sakuyamon is #3 in the mega column.
Note 3: Digimon with a * next to them have further descriptions below the list.
* There are three Agumon in the game. Agumon 1 is Tai's and can digivolve into WarGreymon. Agumon 2 is also Tai's but his Mega is Omnimon. And Agumon 3 is not Tai's and is the color black who digivolves into BlackWarGreymon.
** Imperialdramon Paldadin Mode is the color white and gold and is the Mega of Veemon. Imperialdramon Fighter Mode is the color black and green and is Wormmon's Mega.
*** Gabumon and Agumon 2's Mega forms are Omnimon and they look exactly the same and have no battle differences.