Immortal Champ?

Obviously, with a possibility of dying. I was thinking that this would be an awesome champ idea.

So, I haven't put much thought into the abilities yet, but the idea I came up with is that each ability would have a passive that lowers your armor/MR. Yes, you read that right, Lowers your armor/MR. Your Q/W/E/R would each give a brief moment of invulnerability, increasing the time for each rank, compensating for this. The R would be an area of effect that reverses the armor/magic resist of you and enemy champions caught in the blast. Thus, your negative armor/MR becomes positive, and their armor/MR becomes negative. Suddenly, you become a tank, and they lose all semblance of defense. Combined with your short bursts of immortality, this could lead to a quick pentakill in the right situation, or turn a bad team fight on its side. It would be a particularly hard champion to play well, let down your defenses for a moment and they've one/two shot you. But, when played well, can be nearly impossible to stop. Really a good definition of a glass cannon.

His champion passive ability, not sure on the terminology for it, would make you immortal for 1 second per level 3, 4, 5, 6 seconds at levels 1, 6, 11, 16 respectively, once your health falls below a certain point, making you immune to stuns and slows and, hopefully, giving you enough time to safely escape.

I'm thinking one of his abilities should be a dash, a little overused I know, but it would make for a good quick escape, or rush into a turret for a kill, especially with the invulnerability.

He should also probably have a ranged ability, with his low defense it'd be good to be able to keep your distance.

The last one then, I'm not sure whether it should be a slowing AOE, a shield, or something else. So I'd like to take suggestions on that.

Now, do you think he'd be better suited for AD or AP? Or, maybe, have his abilities scale with health? The lower percentage of health you're at, the more damage you deal? It'd make it a lot more tempting to risk attacking rather than running away after a single hit. Could also make the shield a lot more effective, if we go with a shield. You're nearly dead, and so your shield grants you a few thousand hit points to spare, without actually healing you, so you deal massive damage. Combined with the ult, you might be able to one-shot a fully stacked Cho. I would be pretty excited if this became a thing.

Edit: Just thinking through this, Silence would be a death sentence for him. no abilities, no immortality, easy 1/2 shot