You should be able to beat the Master as a level 23 archmage. Let's see,
this is your character, right?
All right, I can immediately see some problems. You've maxed Bone Armor before Shielding, say -- that's a mistake. Bone Armor is great and you definitely want to max it eventually, but one point is enough early on -- its large cooldown means that it's not as useful IMHO as maxing Shielding, and Shielding makes it stronger
anyway, while also buffing both your Shield runes. Against a boss, your bone armor will run out and then you'll die, while 5/5 shielding helps all the time.
Worse, you've maxed Heal too soon. It's not a bad idea to improve that eventually, but Shielding and mobility are much more important. Going for Reassemble 5/5 before you maxed Shielding or bought more mobility was also a mistake, though it at least gets you an extra life (though you're on Explore, so who cares?) But seriously, what's the point of having a 550-point Reassemble when you have less HP than that? Shielding is your most important defense as an Archmage; you don't
want to be soaking things with your HP. It will happen and you'll want some healing for it eventually, but focus on your shields first.
You should also either pick up Probability Travel, or invest in Phase Door until it's controllable -- possibly both. Up to you whether you want to invest in Probability Travel's rather hefty sustain price, but you need
some way to reliably escape. I can already picture what's happening -- you run out of Bone Armor, you use both your healing options, then you die while they're still on cooldown. More Shielding would help with this by boosting your runes, too, and mobility would help by letting you avoid damage in the first place via keeping out of the Master's way as much as possible. Healing isn't
bad, don't get me wrong, but your Shielding-backed shield runes are a better investment early on, because they don't cost resources, don't take turns, and have a shorter cooldown -- you want your Shielding-backed Shield runes to be the backbone of your defense, setting them on automatic activation, with healing and Bone Armor as your 'oh shit' buttons. (If your shield rune durations are too short for the runic saturation to run out, invest in Resilient Bones.) And you really, really need more mobility -- how did you get this far with no form of controlled escape? Eventually your defenses will run out.
Anyway, with less healing and more shielding + mobility, you'd be able to take out the Master no problem using hit-and-run with Inferno plus whatever other talents you can get off before your defenses start to get low. The Master is nasty but doesn't heal particularly well IIRC, and your shields / cooldown / mana will recover faster than anything he does in any case. He'll summon a lot, but so what, that's what Inferno is for.
Oh, I'd also put a point in Arcane Eye so you can effectively target Inferno from outside of enemy LOS -- although that's a bit cheesy, with that and controlled Phase Door or Probability Travel, the Master is very beatable. Annoying, but beatable.
EDIT: Also, why are you using the big knocker? It's not terrible, but it's really more for Alchemists or for people with weird builds -- it has a decent crit, but its spellpower is lower than your other staff, and more importantly, its +% to physical isn't helping you at all. Also, +spellpower boosts your defenses via Shielding and several other things like that, while +% crit doesn't help you with as wide a range of things. You'd be better off with a staff that boosted your spellpower more and increased the damage types you're using, especially if it had a nice spell itself. Like that staff of blasting you're carrying, say.
