wp_editor

<div class="tumbleboard-tinymce">

    <?php if ( bbp_is_topic_edit() ) : ?>

        <?php
            $post = get_post($post_id, 'OBJECT');
            $tabindex = bbp_get_tab_index();
            $settings = array(
                    'wpautop' => true,
                    'media_buttons' => true,
                    'textarea_rows' => '15',
                    'tabindex' => $tabindex,
                    'editor_class' => 'tumble',
                    'tinymce' => true,
                    'quicktags' => true
            );

            wp_editor( $post->post_content, 'bbp_topic_content', $settings );

        ?>

        <?php else: ?>

        <?php
            $post = get_post($post_id, 'OBJECT');
            $tabindex = bbp_get_tab_index();
            $settings = array(
                    'wpautop' => true,
                    'media_buttons' => true,
                    'textarea_rows' => '15',
                    'tabindex' => $tabindex,
                    'editor_class' => 'tumble',
                    'tinymce' => true,
                    'quicktags' => true
            );

            wp_editor( '', 'bbp_topic_content', $settings );

        ?>

    <?php endif; ?>

</div>