Is this homebrewed shield weapon balanced?

Question

Relatively new player here who likes to theorycraft. Currently playing a homebrew campaign, and I'm thinking of making a backup character for if my current one (a Ranger, who AFAIK are known to be squishy) dies. My DM is fairly lenient, and I want to make a custom weapon for this character. I like the idea of a gung-ho sword and board Battlemaster Fighter, who excels at crowd controlling large groups of enemies (planning on going Vuman and taking Mobile). The intention is to give the character more options when going sword and board, having the versatility to use Maneuvers at melee or at range by using the Throwing Shield (see below).

Throwing Shield
melee weapon (shield), uncommon
AC: +1
Category: Magic Items
Damage: 1d6
Damage Type: Bludgeoning
Item Rarity: Uncommon
Properties: Range, Thrown, Special, Light
Range: 20/60
Weight: 6 lbs.

Special: Needs to be donned beforehand to be used as an attack. Auto unequips (doffs) when used as a thrown attack as part of the Attack action. When used as a thrown attack, the shield immediately returns to the user if the last target it hit is within 60ft of the user. Auto re-equips (dons) when it returns this way. Also gives the user bonus AC when equipped. Manually donning or doffing this shield requires one Action.

Some points I need to make:

• Usually, standard sword and board using any weapon is legal because a shield isn't counted as a weapon, it's a shield, therefore there's no requirement that the weapon you hold in the other hand needs to be a Light weapon.
• However, in this case, RAW, since it's counted as a weapon, the other weapon that you hold in the other hand needs to have a Light property for you to attack with that weapon and the Throwing Shield on the same turn.
• Basically it means that using the Throwing Shield as a weapon (be it ranged or melee) follows the basic rule of two weapon fighting (not the fighting style).
• So, it can't be used as a weapon as long as you're attacking using a weapon without the Light property with the other hand.
• Not viable for the Dueling fighting style when going sword and board.
• Following that, you can still use it as a shield (i.e. granted the bonus AC when equipped) even when you're not using a Light weapon on the other hand.
• Manually donning and doffing this shield still requires one Action. Unless a feat overrides this rule (such as Dual Wielder feat).
• A rare (+1), very rare (+2), and legendary (+3) magic version of this shield exists, the bonus applies to AC, attack rolls, and damage made by this weapon.
  
  
• Variant: 1d8 damage but doesn't have the Light property. Can go Captain America style. Couples well with the Dual Wielder feat.

For simplicity's sake, think of it as a weapon that gives bonus AC, instead of a shield. I actually have a few questions, for both the standard and the variant Throwing Shield, but for the purpose of making it less convoluted, I'll just boil it down to these:
Is this balanced? Are there any weird interactions with feats I'm not aware of?

Bonus question: does lacking the Dueling fighting style makes the sword and board build (specifically this one) considerably less viable?

Answer 1

Not broken, but concerning

My first concern is that it may be a little too strong for Two Weapon Fighting builds (with the shield being used as a regular weapon, not as a thrown weapon), but TWF gets weak quite quickly after 5th level anyway, so this sounds to be an okay buff to that build. The throwing part is flavorful but I doubt it will be seen frequently - you have a decent chance of missing against most enemies (say around \$40\%\$), and that is a high chance when the cost is losing your shieldweapon for the combat. For this reason, I do not think this is overpowered in any way.

My second concern is that this might make a Dueling Sword and Board completely useless when compared to a Two Weapon Fighting Sword and Board. The whole point of Dueling is that you can use a Sword and Board and still get some nice damage buff. So, let us see if our concerns make sense. I will not include the math here, you can check how to compute DPR for TWF and others in my answer in the linked question about TWF.

For comparison, I will be using Point-buy, all ASI is an attribute increase in the relevant modifier (Str in this case) up to 20, and then the ASI are used to increase something non-relevant (such as Con or getting Mobile), and I will be assuming a Fighter, since he gets more extra attacks.

For tier 1 (levels 1 to 4), TWF is always better than Dueling. I mean, strictly better. For any AC, your expected Damage Per Round (DPR) is higher, and you have the same AC. So, yeah, at tier 1, your item made Dueling a useless fighting style, which is a balancing problem.

At tier 2 (levels 5 to 10), with 1 extra attack, Dueling approaches TWF with your shield, but TWF is still superior for every AC. Now, I would get very worried about this. While your item is not broken in any way, its existence made a fighting style completely subpar. Usually, this is not a good call.

Finally, at tier 3 (levels 11 to 16), Dueling finally catches up, being as good as TWF (slightly better, but the difference is less than \$5\%\$.

If you manage to get to 20th level, with 4 attacks per turn for the Fighter, then the gap increases to about \$10\%\$.

Another very important thing to mention is that most campaigns end by 10th level, sometimes going to 14 or 15, and the XP chart is specifically made so the Tier 2 is the one where characters spend more time. Source. This means, for basically the most relevant range of played levels, your item made Dueling a choice that is no longer viable, and it was the go-to choice for Sword-and-board that wanted some damage increment (while Defense is for a more tanky choice).

Ways of going about this that I see:

• Instead of +2 AC, you get only +1 AC. This way, choosing to go TWF has a cost (-1 AC) for the extra damage you are getting, compared to usual Sword and Board builds.
• Make it a Ranged Weapon, so you can not use it for melee two weapon fighting without risking losing the shield. Note: this is a huge nerf and may make it become just worse than regular sword-and-board altogether (although you could still go with Defense as fighting style), but maintains the flavor of the throwing shield.

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Additional comments

I am not sure about making it a regular weapon (i.e. something you can buy in the nearest blacksmith). There are weapons that increase AC, and all of them are magic weapons. On the other hand, these weapons are... weapons, so they stack with an actual shield, while yours is a shield, so using it plus a shield does not stack (see rules on Shields in PHB). Still, since is it clearly better than, for example, a Shortsword, at basically no cost (other than more gp, I guess), it may be worth to consider making it an Uncommon Magic Item.

As mentioned by findusl, a weird interaction is that you can draw the shield as a Free Action (Object Interaction) as part of your attack, throw it, and if it hits, it gets auto-donned. You may want to change that, allowing attacks only if the shield is already donned, or auto-donning on return only if it was already donned.

Answer 2

A weird interaction might be that one could draw the shield as a weapon with the free object interaction and then throw it as an action. On a hit it would return and auto-don, making it a Javelin with a chance to award a free Don shield action.

It is not clear if this is possible, but I think you should forbid it explicitly. Maybe it can only be thrown if donned or only Auto-dons if donned before.