How do I override one animation with another for specific bones in a generic character?

Currently I have an animator controller that controls the characters movement View attachment 533655

I have made a weapon hold animation for a sword, I want that animation to play with the movement. I want the animation to override the movement animations only in the upperbody (head, arms and torso) so that the legs can still move How would I do this.

The character is a generic avatar and I cant make it into a humanoid. I have tried using avatar masks but apparently you need a humanoid character. Is there any other method?

 

Use the Transforms in an AvatarMask instead of the Humanoid section.