I believe the following code should work based on https://piklist.com/user-guide/docs/field-parameters/conditions/

However, everything is being hidden on page load. The entire group.

I’m using Piklist 0.9.5h

piklist('field', array(
	'type' => 'group',
	'scope' => '',
	'field' => '_cn_slider',
	'columns' => 12,
	'add_more' => true,
	'fields' => array(
		array(
			'type' => 'text',
			'label' => 'Title',
			'field' => 'title',
			'columns' => 12
		),
		array(
			'type' => 'textarea',
			'label' => 'Excerpt',
			'field' => 'excerpt',
			'columns' => 12,
			'attributes' => array(
				'rows' => 6,
				'cols' => 12
			)
		),
		array(
			'type' => 'text',
			'field' => 'link',
			'label' => 'Link',
			'description' => 'eg. http://google.com',
			'columns' => 12
		),
		array(
			'type' => 'select',
			'field' => 'is_image_or_video',
			'label' => 'Media Type',
			'choices' => array(
				'image' => 'Image',
				'video' => 'Video'
			)
		),
		array(
			'type' => 'file',
			'field' => 'image_attachment_id',
			'label' => 'Add Image',
			'conditions' => array(
				array(
					'type' => 'toggle',
					'field' => '_cn_slider:is_image_or_video',
					'value' => 'image'
				)
			)
		),
		array(
			'type' => 'text',
			'label' => 'Link to Video',
			'field' => 'video_src',
			'conditions' => array(
				array(
					'type' => 'toggle',
					'field' => '_cn_slider:is_image_or_video',
					'value' => 'video'
				)
			)
		)
	)
));