Make the green player collect the crystal below the rocks. Move the blue player to the space bottom - right of the green player.
Get the green player to shuffle left and right, but don't repeat this with the blue player. Instead, move both players right at the same time until you're at a point where if the blue player moved any further, they'd fall into a hole.
Make the green player collect the crystal below the sticky ball, freeing it, then move out the way. Wait until the sticky ball goes all the way around and falls into a hole.