Hytale mithril doesn't exist yet, but thanks to "suggestions in DMs" endgame mining is going to get "a bit more interesting"

"We are looking at options to make mining a bit more interesting" ...

Hytale's elusive end-game ore, mithril, 'won't be as simple to mine as the others'

"We got some fun ideas".

Hytale's already adding necromancy, improved mining, and better world generation just over a week after launch

It's been just over a week since launch, and Hytale already has its second major update on the way, uncreatively named Update ...
The Escapist

Hytale Mithril Ingots: How to get them, and what you can use them for

By the time players strike out for Mithril in Hytale, they will have reached the best ore the game currently has to offer.
GameSpot

Hytale Early Access Review - Mining The Past

Hypixel's long-awaited survival-crafting game has finally moved beyond its existence as merely a popular Minecraft server to become… a surprisingly familiar Minecraft clone.