How to make your player slide on the ground?

On my project, I’m making an 2.5D Platformer game and one of my actions is to make the player slide on the ground like this example pic of MegaMan.

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The Green box symbolize its colliders recent “Idle” stance. Then when the Player presses a button to slide on the ground which is the Red box that symbolizes the Change of colliders shape when sliding along the axis its facing while playing the “Sliding” animation.

Look at 36:00: Unity 4.0 - Mecanim Animation Tutorial - YouTube