From memory the War Caster feat is the only thing that might work well with this. Its third benefit is:
"When a hostile creature's movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that ...
Generally, only willingly moving out of an enemy's reach provokes opportunity attacks.
From the Basic Rules, p74:
You can make an opportunity attack when a hostile
creature that you can see moves out of your reach. To
make the opportunity attack, you use your reaction
to make one melee attack against the provoking
creature. The attack interrupts ...
Yes, but why it can isn't immediately obvious, though in the case of a Flameskull it's pretty impotent
To make an opportunity attack the monster needs to be able to make a melee attack (PHB, p. 195):
To make the opportunity attack, you use your reaction to make one melee attack against the provoking creature.
Although a Flameskull has no melee attack ...
The verbiage 1/turn definitely allows for the use of Sneak Attack out of turn for the rogue if they somehow get a reaction attack (either granted by an ally or by an opportunity attack).
Note that this basically limits them to 2x per round since you only get one reaction. But yes absolutely. Note that all of the normal restrictions on SA apply, they ...
You are correct.
Tunnel Fighter lets you make opportunity attacks for free, and Polearm Master lets you do so at a distance.
An intelligent or reasonably aware force would have a good chance to figure this out after you skewer the first few.
As for "too good," it's powerful but not unrealistic. Choke points are good strategy in the real world, too; see ...
Reactions can be taken on your turn.
A reaction is an instant response to a trigger of some kind, which can occur on your turn or on someone else's.
Therefore, yes, you can cast Shield as a reaction if you provoke an opportunity attack on your turn.
There are no facing rules in 5e by default. Thus one provokes an OA leaving an opponent's reach no matter how you imagine the characters are faced. The reasoning behind this is that the round represents six seconds of movement: thrusts, parrying, bobbing-and-weaving, &c.*
In your example, the answer is: yes, Atone would provoke an OA from Dip.
If you ...
Yes, but only if the ability forces the enemy to move out of reach using their movement, action, or reaction
The rules state that only when the enemy uses their movement, action, or reaction to move out of your reach will they provoke an Opportunity Attack from you.
From the PHB:
You also don't provoke an opportunity attack when you teleport or when
Yes, reach also determines Opportunity attack range.
Reach (p. 147). This property also
determines your reach for opportunity attacks
with a reach weapon.
— PHB Errata
Most creatures have a 5-foot reach and can thus
attack targets within 5 feet of them when making a
melee attack. Certain creatures (...
Players Basic Rules, pg 71
Moving Around Other Creatures
If you leave a hostile creature’s reach during your move,
you provoke an opportunity attack, as explained later in
Players Basic Rules, pg 73
You can make an opportunity attack when a hostile
creature that you can see moves out of your reach....
As Miniman points out, you cannot grapple as an attack of opportunity because an AoO does not give you an attack action. However, your situation doesn't actually call for an attack of opportunity. Instead, it sounds like you had readied an action. From Basic Rules page 72:
Sometimes you want to get the jump on a foe or wait for
a particular circumstance ...
I would say no. The PHB on page 195 specifically states:
you don't provoke attacks of opportunity when someone or something moves you without using your movement, action, or reaction.
Under the Beast Master archetype on page 93 it says:
You can command the beast where to move on your turn (no action required).
Since the beast counts as something ...
You are correct; movement may be resumed after an Attack of Opportunity.
Movement is "spent" by the foot; as in, if a creature has a movement speed of "30ft", then they can spend that much speed during a move action. If they are interrupted by an opportunity attack after 10ft, then they still have 20ft left to spend.
To further support this, look at the ...
From the section on opportunity attacks:
You can make an opportunity attack when a hostile creature that you
can see moves out of your reach. To make the opportunity attack, you
use your reaction to make one melee attack against the provoking
creature. The attack interrupts the provoking creature’s movement,
occurring right before the creature ...
The rules for reactions are fairly straightforward:
Certain special abilities, spells, and situations allow you to take a special action called a reaction. A reaction is an instant response to a trigger of some kind, which can occur on your turn or on someone else's. The opportunity attack, described later in this section, is the most common type of ...
You only get ONE reaction between the start of your turn and the start of your next turn.
An Opportunity Attack is considered a Reaction (PHB pp195)
You can make an opportunity attack when a hostile creature that you can see moves out of your reach. To make the opportunity attack, you use your reaction to make one melee attack against the provoking ...
Usually a creature has only a single opportunity attack available
To make an opportunity attack a creature needs to use their reaction to do so. From the rules on opportunity attacks (emphasis mine):
You can make an opportunity attack when a hostile creature that you can see moves out of your reach. To make the opportunity attack, you use your reaction ...
No, with a caveat.
No, because Mage Slayer doesn't name this reaction an opportunity attack, so it doesn't count for triggering Sentinel.
The caveat is that, well it sure looks like an opportunity attack, RAW aside, so your DM may very reasonably say that it is. So bet on "no", but this is likely an easy house rule to get out of your DM if you bring it to ...
On a failed save, the creature must choose a new target or lose the
attack or spell. (PHB 272)
While it is not explicitly stated, it is a reasonable assumption you have to choose a valid target for your attack (or spell). Like, the spell description does not say, but obviously you must choose a target within range. A valid target for an opportunity attack ...
According to third edition designer Skip Williams, in his article Attacks of Opportunity (Part One), D&D uses attacks of opportunity to add tactical complexity and danger, to discourage certain actions in combat without banning them outright, and to balance out useful or powerful combat manoevers:
The D&D game uses its attack ...
No, you can't provoke opportunity attacks this way. From the Player's Basic Rules, page 74:
You also don’t provoke an
opportunity attack when you teleport or when someone
or something moves you without using your movement,
action, or reaction. For example, you don’t provoke an
opportunity attack if an explosion hurls you out of a foe’s
reach or ...
From page 74 of the Basic Rules (also PHB p.195, or this SRD site):
[...] You can avoid provoking an opportunity attack by taking the Disengage action. You also don’t provoke an opportunity attack when you teleport or when someone or something moves you without using your movement, action, or reaction. For example, you don’t ...
There is no Opportunity Attack
The Polearm Master Feat is clear that the reactionary attack is an Opportunity Attack, and Disengage says that your movement doesn't cause Opportunity Attacks.
In your example, moving into a Polearm Master's reach while Disengaging doesn't trigger the Feat's Opportunity Attack. Think of it as sort of batting away the guy's ...
D&D is a consensus game - Discuss the Options
Your problem is not unique - it happens to every game master with a new system. It even happens in board games. It also happens whenever there is errata - changing the "offical rules."
But, you are playing with a group of people so you should discuss any rule changes with the rest - regardless of the the ...
Yes, use the actual rules now that you know them
The game is balanced around the ruleset it assumes is in use, and as you've already noticed any change to the rules is going to have system-wide implications (in this case, some very significant ones). You'll find a lot of powers, items, feats, and design philosophies make more sense now.
But allow massive ...
No, it's not an opportunity attack
The relevant phrasing in the Sentinel feat (PHB, p. 169-170) is:
When you hit a creature with an opportunity attack, the creature's speed becomes 0 for the rest of the turn.
So the prerequisite for this feature is that you must hit a creature with an opportunity attack.
The relevant phrasing in the War Caster feat (...
In all cases, the Attack of Opportunity is resolved in the square in which the provoking action is performed.
In the case of movement, the act of moving out of a threatened square is performed in the threatened square - other squares do not come into play until that part of movement has been resolved.
This is not abundantly clear from the rules on Attacks ...
Yes, they can.
From the spell:
If you issue no commands, the creature only defends itself against hostile creatures. Once given an order, the creature continues to follow it until its task is complete.
If you order your animated objects to "Kill those orcs", they will do everything they can to accomplish the task until it is complete without you ...
No, it's not an opportunity attack.
An opportunity attack is a specifically named game mechanic with specific rules set out for it (as found on page 195 of the PHB).
If the Sentinel feat was meant to be an opportunity attack it would say something like:
[...] you can make an opportunity attack against the attacking creature.
As it's written it's not ...