Using Beetlemon/Blitzmon, first activate the Digivolution to Metal Kabuterimon/Bolgmon. Then, use the B-Down attack, but hold B. Almost always, three spirit balls (each worth 3) and one Ancient Spirit Diamond. Using this correctly, you can use the Ancient Form twice before the Digivolution time runs out.
To unlock ex-Agunimon, beat the game with all six characters and collect 800 or more spirits with Agunimon, Kazemon, and Kumamon.
To unlock Ex-lobomon clear the game with all six characters, and collect 800 or more spirits with Lobomon, Beetlemon, or Lowemon.