Diaboromon is a Digivolution of BlackWarGreymon and GranKuwagamon, both at level 99. You need to get those two. For BlackWarGreymon, first gain her mega, Sakuyamon. Then level her up to level 10 to get Devimon. Level Devimon up to level 50 to Digivolve to Myotismon (level 99 MaloMyotismon). Before letting Myotismon's skill level reach 20, make sure that Renamon's strength is over 300 or you will not get Grizzmon. Once you have Grizzmon, when its skill level is 30 and defense is over 280 (without any armor or accessories), you will get Greymon. Greymon turns into SkullGreymon at skill level 50 with Dark Tolerance over 250. When SkullGreymon reaches level 99, it becomes BlackWarGreymon, which then needs to reach level 99 itself. For GranKuwagamon, once Kyubimon reaches level 20 and has over 80 strength, Stingmon will appear. When Stingmon reaches level 40, Kabuterimon will become optional. The other Digimon besides Kabuterimon required to get GranKuwagamon is Imperialdramon, which is Paildramon at level 40. Paildramon is ExVeemon and Stingmon and level 5 (if you have Kabuterimon there is no need to worry about Stingmon for this). Raise Renamon to her ultimate, Taomon, and have Taomon's skill level reach 20 with her wind tolerance over 120. Once you have Kabuterimon and Imperialdramon, level them both to level 40 to get GranKuwagamon. Note: The Digivolutions explained here, such as Greymon to SkullGreymon and BlackWarGreymon can be done with their original Digimon (i.e. Agumon for Greymon, etc.)