The Hero’s Graves locations in Tunic can be found and activated early on in the game, but they won’t be useful until after the first confrontation with The Heir. After losing the initial battle, the fox returns to the beach in the Overworld as a ghost, with none of their previously applied stat upgrades. To return to corporeal form and restore any stat boosts, players must visit each of the six Hero’s Graves scattered around the world of Tunic.

https://screenrant.com/tunic-heros-grave-locations-guide-stat-upgrades/