Duke Fishron is a Hardmode boss. While he can be summoned as soon as Hardmode is initiated, he can pose a serious threat to new or underprepared players and should be fought later on in the game. Some players may challenge him with post-mechanical bosses gear, but most players may want to wait until post-Golem to battle him. Fighting Duke Fishron is completely optional and not required for game progression, but his defeat will reward the player with powerful weapons.