How MUch?

Quote from tironi >>

How MUch?

I assume you mean how much does it cost? 

If so, then I would say it depends on your DM. Since magic item buying/selling is mostly left up to DM discretion in 5e. However, if we go by Xanathar's Guide's guidlines on the subject. It is a rare magic item, so the asking price would come from this: 2d10 × 1,000 gp. However, most DMs know how powerful AC is, so they might skip the roll, and assign it a price at the higher end.

Some DMs don't even allow magic item's to be bought like other gear, others allow it, but decide which ones are available randomly. 

So just having the thing on your back, gives you a +2 to your AC.

You don't even have to be proficient.

Awesome! 

Not if your DM goes by the rules:

- The item description say: "While holding this shield, [...]". So, just having it on your back doesn't do anything.
- It also doesn't waive the usual requirement for Shield Proficiency. So, RAW would apply https://www.dndbeyond.com/sources/basic-rules/equipment#ArmorandShields

But, as always, if you can convince you DM otherwise... ;)

Actually  no...

Rules as written a plus 2 shield conveys it's plus 2 anyway. No holding or proficiency required.

So, this shield has +2 AC because it's a shield, and another +2 due to its enchantment.

- Based on the first line of this item's decriptions, you only get its additional +2 AC enchantment when you are "holding this shield".

- And based on the second line of the decription (which is quoted from the Basic Rules for Shields https://www.dndbeyond.com/sources/basic-rules/equipment#Shield), you don't get the base +2 AC from just wearing it on the back, either, because you need to wield it.

So, as far as RAW go, you need to hold/wield any shield you want to benefit from. And while you don't need proficiency to hold it, you would have disadvantage on any ability check, saving throw, or attack roll that involves Strength or Dexterity, and you can't cast spells. (https://www.dndbeyond.com/sources/basic-rules/equipment#ArmorandShields)

Again, if the DM doesn't mind that's fine, but that would be a homebrew rule.

hiva

Lol tight