Season 14 gives you two recipes for crafting a Mythic Unique. Enter what you're holding — the planner tracks both paths, tells you exactly what's missing, and remembers your counts between visits.
Season 14 turned Mythics from pure drops into a crafting target, and the two recipes serve different situations. The Horadric Cube's "Upgrade to Mythic" takes a Unique of 850+ item power plus 5 Pandemonium Fragments and upgrades that exact item — same slot, deterministic — into its Mythic version with +30% Unique Power and the other affixes rolled at maximum. It unlocks at level 70 in Torment difficulty or higher. Because the output is same-slot, this is the targeted path: the base you feed it is the Mythic you get.
The Jeweler path — 3 Resplendent Sparks and 15 runes — exists for when you don't own a strong base in the slot you're chasing. It's the more expensive route in raw material rarity, but it doesn't ask you to first farm the 850+ Unique.
Fragments come from the seasonal loop: finish the "A Gospel of Despair" questline, then run Pandemonium Ruptures into the Realmwalker and Deathtoll Chambers — Fragments accumulate through that circuit alongside Superior Lair Keys. Once crafted, your Mythic isn't finished: Season 14 also lets Mythics be Enchanted and Tempered, which is where the last chunk of power lives. For the wider crafting system, see the Horadric Cube guide.
No — it upgrades the specific 850+ Unique you feed it, same slot. That's the whole point of the path: bring the item you actually want as a Mythic.
Yes, locally in your browser — come back mid-season and your material counts are where you left them. Nothing is sent anywhere.
The recipe cost is 15 runes alongside the 3 Sparks. Rune values differ wildly on the market, so feed it your cheap ones — the recipe doesn't reward premium runes.
That depends on your build — check your class's expanded card on the tier list for its S14 build guides, which list the Mythic priorities per build.