Can someone explain why there's sometimes that they don't draw the frame completely? I want to learn

You mean the shadows? Its because the one doing 2gen for the cut can look at the keyframes WITH shadow and then apply them accordingly to the ones missing them.
When parts of the frame is copy-pasted with red outlines, its because they are indicating 合成 or 同トレース.

AlfaAuveron said:
Can someone explain why there's sometimes that they don't draw the frame completely? I want to learn

That is because the keyframe and the interpolation animator did only the most important parts and left the role to draw the rest for the clean up team.

Habarudo said:
You mean the shadows? Its because the one doing 2gen for the cut can look at the keyframes WITH shadow and then apply them accordingly to the ones missing them.
When parts of the frame is copy-pasted with red outlines, its because they are indicating 合成 or 同トレース.

so when they don't draw something for example at 00:12 where Power's body disappears, it means that the body is the same as the previous frame and they only draw the changes right?

Man I love Michaels volume and flow of his smoke.