With my new hardcore harbinger league Shadow, I did manage to get Fire Nova as suggested in the build linked by @Bateau.
Wow, Fire Nova is something I’d never tried before, and it’s strong right from the beginning. This is not something that gets strong slowly over time. And honestly, his passive tree path doesn’t even lead to that many nodes about Mines, it’s mostly all about going all over the tech tree for some mine nodes and some area of affect nodes and a bunch of life nodes. So pretty much the strength of the build is not in the passive tree, but in the Fire Nova Gem itself. That’s the kind of build I like!
I almost got killed though. The new version of the chick you fight at the end of Act 1, the one that turns into a different form, she’s become really tough now compared to last time I played the game. She does a ton of cold damage in her first form. So my big advice to hardcore players for Act 1: Try to find cold resistance as much as possible.
I was out of health potions completely, running around laying fire traps and shooting frost blades at her as much as I could (I didn’t have Fire Nova mines yet, it was a quest reward for killing her). If I’d gotten hit one more time it would have meant another dead Shadow. But I got her. And once her first form dies, you get some health potions back.
The whole “running around dodge attacks from a boss” part of the game is really unsatisfying using the mouse by the way. When I’m doing that against Mathael in Diablo 3, it’s much more satisfying because it’s with a controller, and you can use the dodge move as well. When you’re just clicking areas on the screen in PoE using your mouse, it’s much, much less satisfying, and much easier to misclick and make a mistake (like when I died doing that weird Ascendancy Trial against all those spiked blades on the ground).
Anyway, what I’m saying is that the way they’ve designed the ascendancy trials and boss fights, I’m actually looking forward to the Xbox version of this more now, since it should be more satisfying to play those areas with the controller.
EDIT: Btw, why am I playing the PC version again instead of the Xbox beta? Because there’s no Harbinger league on Xbox for some reason. They just have standard and hardcore in the current beta. The Harbinger enemies make the levels a lot more interesting, even though I agree with @Misguided about the inventory clutter they’ve added being annoying in this league.