When fighting the tail, have a Digimon with good power. Galacticmon is weak against fight attacks. The attacks that weaken him the most are Thunder attacks. Just before you defeat the tail, have your weakest Digimon out. The tail will disappear and the body will use a attack called Gracnark Cannon. Your Digimon's HP will go down to one and Galacticmon will copy one of your attacks. Next, fight the body. This is very difficult. Nothing does a lot of damage on him. Thunder attacks still work well. When you only use fight enough times he will stop attacking for awhile, but his main attack is to counter attack then hit you with a attack called "????????". It does not do that much damage. After you have hit him enough times an FMV sequence of him exploding will begin.