An example WP plugin to show how to register TinyMCE plugins in WordPress

tinymce-example-plugin.php

<?php
/**
 * @package TinyMCE_example_plugin
 * @version 1.0
 */
/*
Plugin Name: TinyMCE example plugin
Plugin URI: http://wordpress.org/extend/plugins/#
Description: This is an example plugin 
Author: Your Name
Version: 1.0
Author URI: http://example.com/
*/

/**
 * Filters TinyMCE buttons
 *
 * @since 2.0.0
 *
 * @param array  $buttons First-row list of buttons
 * @param string $editor_id Unique editor identifier, e.g. 'content'.
 */
function example_plugin_register_buttons( $buttons ) {
	$buttons[] = 'table';
	$buttons[] = 'prism';
	return $buttons;
}
// add new buttons to the first row
add_filter( 'mce_buttons', 'example_plugin_register_buttons' );

/**
 * Filters the list of TinyMCE external plugins
 *
 * @since 2.5.0
 *
 * @param array $external_plugins An array of external TinyMCE plugins
 */
function example_plugin_register_plugin( $plugin_array ) {
   $plugin_array['table'] = plugins_url( '/mce/table/plugin.min.js', __FILE__ );
   $plugin_array['prism'] = plugins_url( '/mce/prism/plugin.js', __FILE__ );
   return $plugin_array;
}
// Load the TinyMCE plugin
add_filter( 'mce_external_plugins', 'example_plugin_register_plugin' );