Detectar una palabra dentro de una cadena

[Death_Empire]

puedes usar strpos http://php.net/manual/es/function.strpos.php

o otras funciones para los string
* strrpos() - Find the position of the last occurrence of a substring in a string
* stripos() - Find position of first occurrence of a case-insensitive string
* strripos() - Find position of last occurrence of a case-insensitive string in a string
* strstr() - Find first occurrence of a string