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$cmb_select_slider->add_field( array(
	'name'             => 'Elija el slider para Móvil',
	'id'               =>  $prefix . 'mobile_metabox',
	'type'             => 'select',
	'show_option_none' => true,
	'default'          => 'custom',
	'options_cb'       => 'get_masterslider_names', //aqui esta la magia
));

<?php
	$slider = get_post_meta(get_the_ID(), 'kiaplazasite_mobile_metabox' , true);
 ?>
 
 <?php echo do_shortcode( '[masterslider id="' . $slider . '"]' );?>