(And a piece of fanfic.)

See, I suppose this happens if an attack hits during a Biomerge: An error occurs and corrupts the data, making the result an "alternate" fusion of Tamer and Digimon, but this time, closer to the Tamer's shape.

Shown here is Knolemon, Guardian of Knowledge. He was testing his "digiCore Theory" after he gave his own data to save Tentomon. In returning to the Digital World, Tentomon's data collided with his "empty shell", his data-less body, fusing the two.

....He's also in a band.