Freyr'sAntler is an item he uses for fighting to replace his stolen weapon, Ingrid.
Norse Mythology[]
The most extensive surviving Freyr myth relates Freyr's falling in love with the female Jötunn Gerðr. Eventually, she becomes his wife but first Freyr has to give away his sword, Ingrid, which fights on its own "if wise be he who wields it." Although deprived of this weapon, Freyr defeats the Jötunn Beli with an Antler. However, lacking his sword, Freyr will be killed by the fire Jötunn Surtr during the events of Ragnarök.
God of War Series[]
Freyr's Antler is the object he used to replace his sword Ingrid that was stolen by Odin. Freyr can be seen using it for fighting and self defense in the game. The Antler has grey wrappings around it, likely to create some sort of grip for him to wield it better, the Antler also appears to have either carvings or Norse patterns written into it. Freyr fashioned the Antler on the right side of his hip. He likely retrieved it from Vanaheim. His Antler is also a direct reference to Freyr, losing his sword Ingrid in Norse Mythology.
Trivia[]
Freyr's Antler is a direct reference to him losing his sword, Ingrid in Mythology and replacing it with an Antler so he can fight/defend himself.