To use Override Animator Controllers, follow these steps:

1. Create a normal Animator Controller that will be used as the reference controller containing the logic of animation states. In the provided example, it is the HumanCombat controller, created with Warrior animations.
2. You can attach this controller to your first character (its Animator component) and use it as previously.
3. Create an Override Animator Controller by right-clicking on the Project View and choosing Create | Override Animator Controller.
4. Select the newly created override controller and go to the Inspector tab.
5. Drag and drop your original/reference Animator Controller to the Controller field of the newly created override controller.
6. You will see all your original animation clips listed on the left and fields for overriding those animation clips.

7. Drag and drop the animation clips from your second character to the override fields corresponding with original animation clips of your first character. In the provided example, Human animations are replaced with Spider animations.
8. Assign the Override Animator Controller to the Controller field of the Animator component of your second character.