ShNURoK42

   protected function bbcode($bbcode)
    {
        $bbcode = str_replace("\n", "  \n", $bbcode);

        $bbcode = str_replace("[b]", "**", $bbcode);
        $bbcode = str_replace("[/b]", "**", $bbcode);

        $bbcode = str_replace("[i]", "*", $bbcode);
        $bbcode = str_replace("[/i]", "*", $bbcode);

ShNURoK42

<?php

class MyParsedown extends \Parsedown
{
    function __construct()
    {
        $this->InlineTypes['@'][]= 'UserMention';

        $this->inlineMarkerList .= '@';
    }