This is a very minimal plugin that does nothing but increase your site's Geek Factor.

Directory Structure

mantis/
  plugins/
    Supercow/
      Supercow.php

plugins/Supercow/Supercow.php

<?php
 
class SupercowPlugin extends MantisPlugin {
 
  function register() {
    $this->name        = 'Super Cow Powers';
    $this->description = 'Gives your Mantis installation super cow powers.';
 
    $this->version     = '1.0';
    $this->requires    = array(
      'MantisCore'       => '1.2.0',
    );
 
    $this->author      = 'Fred Smith';
    $this->contact     = 'fredsmith@fredsmith.fsn';
    $this->url         = 'http://fredsmith.fsn';
  }
 
  function init() {
    plugin_event_hook( 'EVENT_PLUGIN_INIT', 'header' );
  }
 
  /**
   * Handle the EVENT_PLUGIN_INIT callback.
   */
  function header() {
    header( 'X-Mantis: This Mantis has super cow powers.' );
  }
 
}

This is a plugin that detects svn:123 and hyperlinks it to the ViewVC web page that contains all the details of the changeset.

plugins/svnlinks/register.php

<?php
 
/**
 * Return plugin details to the API.
 * @return array Plugin details
 */
function plugin_callback_svnlinks_info() {
  return array(
    'name' => 'SVN Links',
    'description' => 'Detects references to SVN changesets and hyperlinks them.',
    'version' => '1.0',
    'author' => 'Victor Boctor',
    'contact' => 'vboctor -at- users.sourceforge.net',
    'url' => 'http://www.mantisbt.org',
  );
}
 
/**
 * Intitialize the plugin.
 */
function plugin_callback_svnlinks_init() {
	plugin_event_hook( 'EVENT_TEXT_LINKS', 'string_display_links' );
}

plugins/svnlinks/events.php

<?php
 
# Configuration:
# $g_plugin_svnlinks_svn_changeset_link = 'http://mantisbt.svn.sourceforge.net/viewvc/mantisbt?view=rev&revision=%s';

/**
 * Handle the EVENT_TEXT_LINKS callback.
 */
function plugin_event_svnlinks_string_display_links( $p_event, $p_string ) {
	$t_svn_changeset_link_format = config_get( 'plugin_svnlinks_svn_changeset_link', '' );
	if ( is_blank( $t_svn_changeset_link_format ) ) {
		return $p_string;
	}
 
	$t_svn_changeset_link = sprintf( $t_svn_changeset_link_format, '\\1' );
 
	$t_replace_with = '<a href="'. $t_svn_changeset_link . '" target="_new">svn:\\1</a>';
 
	return preg_replace( '/svn\:([[:digit:]]+)/i',
						 $t_replace_with,
						 $p_string );
}