Fire Emblem: The Sacred Stones/Chapter 15: Scorched Sand

A surprisingly hard chapter. Meet up with Eirika's group using some flying and magic users, kill Caellech, then go kill Valter, cautiously. If you have the time and patience along with a summoner, it is possible to endlessly summon warriors to wear down Vaulter's(or any other boss's) weapons. Grab the things hidden under the sand using a thief/flying unit combo.