Off with Its Head!

Simply decapitate a medusa - climb onto her with R2/RT and hack at the head and neck with a melee weapon until it comes off. Do it while she's still fairly healthy and you'll bag 487228022 (a Preserved Medusa Head) at the same time; leave it until she's nearly dead and you'll still get this, just not a usable head. She lives in the Calignious Depths, south of Bakbattahl.