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Magpie Barbarian is a hilarious concept and seems like a very strong class- being able to make that BA unarmed strike at all times (even if holding another weapon) leaves Berserker in absolute shambles, although Berserker isn't very good anyways so that's not a huge deal. The junk weaponry stuff is really entertaining and creative.
But the real meat of the class is level 6. One thing that I can't stress enough is Utility, Utility, Utility! It's everything about why Wizards are so gamebreaking and why default default fighters and barbs can end up feeling mediocre. Level 6 lets you apply a lot more strategy in combat, although I do note that the latter three Barbaric Exploits are much better than the others- Sapping Strike makes it hard for enemies to reposition effectively without using magic, Shielding Parry can shut down Fireballs and dragon breath completely (comboes very nicely with Danger Sense), and Terror Display may be legitimately overpowered- Fear Auras have massive potential to shut down encounters, and being able to pop one repeatedly if you're good at securing kills can absolutely break a lot of encounters. All it needs for balance is that enemies who save against the aura become immune to future uses of the feature for that day.
Marauder and Junk Warrior are neat and fit the class, nothing more to say about them.
Purple Dragon v2, seems good.
Undying v2... The level 1 feature is pretty funny (and also destroys the game if you play with lingering injuries, but most DMs don't do that) but not particularly powerful. Among the Dead, pretty good but it's definitely carrying the subclass and doesn't carry it that hard. Undying Nature is basically worthless (Protection from Poison is super easy to get at that point, and you don't see that much elemental damage anyways, this thing could make you Poison Immune and I'd say it was pretty 'meh'). Indestructible Life, meh. And then... Phylactery. Holy FUCK that is a strong capstone feature. The problem is that the rest of the class sucks, and reaching all the way up to level 14 with an otherwise weak class is a daunting prospect, to say the least.
Anyways, all told, 7.9/10 homebrew which I would be willing to allow at my table, good show sir!