Omegamon SP event.
You had to get WereGarurumon and MetalGreymon and evolve them to Metalgarurumon and Wargreymon and then, fuse both to get Omegamon God+, which you evolved to Omegamon SP.
The catch: Both WereGaruru and MetalGrey needed specific grains to evolve, so you had to farm those, and in the event, both frags droped with no restriction, so there were cases where players had all Metalgarurumons ready, but needed the frags for Wargrey.
Also, to evolve to Omegamon SP, you needed an Omegamon God+ at max lvl as a material.
Oh, and there was also caps, which could screw your drpos even more.
All of that for a mon with a half the dmg received skill as main.