see: http://www.fantasicaunofficial.com/t4776-panel-trials-of-sol-lune-feb-28th-march-8th
there's a link to JP site which has the info.
but usually its the last boss -- in this case, black dragon.
and ever considered asking at the event thread? event thread is at: http://www.fantasicaunofficial.com/t4772-panel-trials-of-sol-lune-feb-28-mar-8