Prone was an excellent choice
You said that the cleric wanted "to stop [the ghoul from] hitting people and make it easier to hit." The prone condition has the following two applicable features:
The creature has disadvantage on attack rolls.
An attack roll against the creature has advantage
if the attacker is within 5 feet of the creature. ...
While a shield can be indeed made of metal, you are wielding it, not wearing it.
In the equipment chapter (p. 144) the PHB refers to a wearer of armor, but says you wield a shield.
"Rules Answers: March 2016" from Wizards of the Coast points out that "various various game features distinguish between the armor you wear and a shield you wield." It provides ...
A general preface: each edition of D&D is its own game, and rules should be evaluated as such. Just because things happened in old rule sets does not mean that it will in 5e. Though it can be helpful to look at old editions for inspiration, you should be careful of the rules environs of the edition you are trying to modify when making house rules.
It's not that easy. Donning or doffing a shield costs an action: see the table on Player's Handbook page 146. Therefore most characters cannot don a shield after making an attack or doff the shield before the attack - they need a second action to do one of these, and two extra actions to do both.
No! The shield is not a weapon, this is designed to be a sword and board feature.
Shield is definitely not a weapon (no weapon stats), and there are currently no enchantments to make it a weapon. This is a feature designed for a brawler style (hand free for grappling) or a sword and board fighter.
No (but your DM can allow it)
Player's Handbook, p.144:
You can benefit from only one shield at a time.
It doesn't say you only gain the AC bonus from one shield, it says you cannot benefit from more than one shield. If you attach a second shield, only one of your shields has effect (unless a more specific rule elsewhere overrides that).
Note that it ...
The relevant rule in the armor section states:
You can benefit from only one shield at a time.
This means that only one shield serves to give you any benefit (including the ones from the Shield Master feat).
This is further backed up from this Sage Advice page from the lead designer, Jeremy Crawford (thanks @V2Blast in the comments)
No matter ...
10% is the naive answer
The +2 bonus to AC is 10% of the d20 roll, but it is more complicated than that:
If the enemy can only hit you on a natural 20, adding a shield does not do anything
If without a shield the enemy hits you 50% of the time, it becomes 40% with one. The difference is about 20%1.
If the enemy only misses on 1, dropping the shield does ...
The Animated Shield says that it
protects you as if you were wielding it.
This strongly implies that you aren't wielding it.
The Monk's Unarmored Defense feature works
while you are wearing no armor and not wielding a shield.
So the use of an Animated Shield shouldn't interfere.
As for proficiency, the only requirement for using an Animated Shield ...
I think you're bypassing the "don" and "doff" rule for shields.
I agree that there's daylight to be seen between carrying and "wielding" a shield. But I'll pose you this question: if you can have a shield and switch states from "wearing" to "wielding" it freely, then what is donning or doffing?
As for the comparison to equipping a weapon, I don't think it'...
A shield requires an arm, not just a hand, to wield:
Anyone can…strap a shield to an arm.
PH, Armor and Shields, p. 144
This jibes with real-world use of the large shields, where the arm provides necessary support to make the shield useful. (Bucklers, or hand shields, may be a different issue, but there are no bucklers in official D&D 5e rules.)
A magic item meant to be worn must be donned in the intended fashion: boots go on the feet, gloves on the hands, hats and helmets on the head, and rings on the finger. Magic armor must be donned, a shield strapped to the arm, a cloak fastened about the shoulders. A weapon must be held in hand. (Pg. 140 DMG, emphasis mine.)
Also Rare Exceptions Exist. If the ...
A shield is an item. You can pick up an item without an action (Player's Handbook p.190).
Wielding a shield, not merely holding it, increases your Armor Class by 2 (Player's Handbook p.144). Donning a shield takes an action. (PHB p.146)
PHB p.146 says that armor must be donned to benefit from it.
If we wish to be exceptionally literal, p.144 says ...
You can use a staff and shield, because you can use staves one-handed anyway
A quarterstaff is a simple melee weapon with the versatile property, meaning that you can wield it one-handed without penalty - it just does slightly more damage if you use it two-handed:
Versatile. This weapon can be used with one or two hands. A damage value in parentheses ...
Yes, you can cast spells with a Material (M) component without issue.
Your Holy Symbol takes care of it.
This is one of the more difficult things to look up in the current 5e rules. It starts on page 58, under Cleric spellcasting:
You can use a holy symbol (found in chapter 5) as a spellcasting focus for your cleric spells.
In the equipment section, ...
You take the lowest of the two maximum dex bonuses.
As GMJoe noted, they aren't giving you a dex bonus, they're setting a maximum on your dexterity bonus to AC. As in, you cannot have a higher dexterity bonus to AC while using that item. If you have armor with a max dex of +1 and a shield with a max dex of +2, then the highest dexterity modifier your AC can ...
In core folks do this with their tower shields
A creature fighting a dragon can take the ready action specifying the action as I gain total cover from my tower shield and the condition as When the dragon is about to use his breath weapon. When the condition's met and the dragon uses its breath weapon anyway, most dragons' breath weapons no longer have line ...
The rules for shields say:
Shields. A shield is made from wood or metal and is
carried in one hand. Wielding a shield increases your
Armor Class by 2. You can benefit from only one shield
at a time.
So as far as the rules are concerned, a shield only counts if you're carrying it in one hand. If it's on your back, it's effectively worthless.
No, wearing a shield does not count as Armor
Shields are in the Equipment section (Chapter 5) of the PHB, but are not classified under the Armor section when determining Light, Medium, or Heavy Armor.
The posted Sage Advice also contains some details differentiating Shields from Armor:
These methods—along with any others that give you a formula for ...
By strict RAW, no. Allowing it wouldn't harm your game meaningfully, however.
Shields are in the armour category, and are thus not weapons. You could easily argue that you could use it as an improvised weapon, but that does not make it an actual weapon. Using improvised weapons as justification for doing this does not hold up, as that would allow you to ...
Tower shields are not always bad. I've seen them used without being a hindrance (by someone who made a build around never having to make attack rolls). They're usually bad, though.
For one thing, it weighs 45 pounds. Not a problem for a 20 STR character, but it can by itself cause encumbrance for a weaker character.
It's armor check penalty is ...
Yes, because a shield is not armour
The shield in the equipment chapter is in a different category than light, medium, and heavy armour, and in the classes section shields are listed as a separate proficiency than each of the light, medium, and heavy armour.
Also PH page 14, Armor Class, mention wearing armour and carrying a shield several times. Note that ...
The actual rules for this are oddly worded, but the notation is pretty simple.
In general, there are two formats for "things that increase your AC." The most common format is the one attached to armor:
[your AC equals] 11 + Dex modifier
or Draconic Resilience:
your AC equals 13 + your Dexterity modifier.
Note that there is no "plus" at the ...
After: You choose to use the feat after successfully saving
Here is the order of events as per the rule you quote:
1) You find yourself in a fireball's area of effect.
2) You get to roll your Dexterity saving throw.*
3) "If you succeed" on this saving throw you "can" use your reaction to get the feat's benefit.
[The "bold quotes" here are straight from ...
Unless an exception is specified, chapters 5 and 7-12 of the Players Handbook apply to monsters as well as player characters. This means that a monster does need to take an action to don or doff a shield.
Whether or not a monster is already wearing a shield when first encountered is decided by the DM. For example, a DM may decide that unless a creature is ...
Shield is not one of the available options for an arcane focus. You're 100% in house-rule territory.
One of the reasons for allowing Clerics (and Paladins) the use of a holy symbol on a shield is because it's not fundamentally different from any other use of a holy symbol - wearing a holy symbol is sufficient (Holy Symbol, PHB p151).
Other focuses must ...
RAW, Your hand is occupied.
The description of a Shield in the PHB states...
Shields. A shield is made from wood or metal and is carried in one hand. Wielding a shield increases your Armor Class by 2. You can benefit from only one shield at a time.
Emphasis Mine from PHB p144
Thus, the PHB seems to be referring to shields that are 'held' with the hand, ...
Use thrown finesse weapons and the Sharpshooter feat
Thrown weapons only require one hand to draw and throw. You can use your free object interaction each round to draw a new one each round. This just requires you to be carrying enough to get through a combat encounter or two.
As a rogue, most of your damage will be coming from Sneak Attack, so the smaller ...
Everybody needs a martial weapon proficiency
The shield bash rules say this (emphasis mine):
You can bash an opponent with a light shield or heavy shield, using it
as an off-hand weapon. See Table: Weapons for the damage dealt by a
shield bash. Used this way, a shield is a martial bludgeoning weapon.
For the purpose of penalties on attack rolls, ...
You could use the Help action for this
"I trap him between my shields" seems like an excellent way to describe how your help is giving someone else Advantage on an attack, and that's exactly what the Help action offers. And everyone can do it.