I haven’t play since season 3 to 4, because I am stuck at t70 for end game.

First to have runes you need the extension

Best way to have runes are bosses and spark by reclycling your mythic item that you don’t want.

Mythic items are special uniques like Shako, or you mean they can be mythic of regular unique item?

no. they can only be dropped by bosses and have like a 1% drop rate and are random. can not upgrade from a unique.