Mastery after maxing skills
Reaching maximum level in all five skills opens the Mastery Cave, where extra experience can unlock skill masteries and their specialized rewards.
How it works
The Skills passage says the Mastery Cave becomes accessible after all skills reach maximum level. Extra experience contributes to mastery progression, and mastering each of the five skills unlocks listed perks or recipes, including the Iridium Scythe, Heavy Furnace, Treasure Totem, Advanced Iridium Rod, and trinket equipment slot.
When it helps
If all five skills are already maxed, consider which mastery reward fits your next activity: farming, mining, foraging, fishing, or combat. The supplied evidence does not compare rewards by value.
The tradeoff
Mastery is a later system with an all-skills threshold, so its choices do not apply before that access condition is met.
Your next step
Once all five skills are maxed, visit the Mastery Cave and review the reward tied to the skill you want to specialize.
Read the supporting references
A focused reference to tool upgrades, skill progression, Farming professions, and Mastery in Stardew Valley. The supplied Skills history lists changes through version 1.6.9; Tools includes version notes for specific changes, but does not establish the version of all mechanics described here. Guidance explains the referenced mechanics; it is not a tested damage ranking. Check the stated edition and source version before applying a patch-specific detail.