D&D 5E [Rules Question] Opportunity Attacks and Total Cover

[Tormyr]

I would absolutely not grant an opportunity attack.

An important part of the xorn's power is the ability to maneuver unimpeded. It's what makes the monster a threat. Otherwise you're just fighting an ogre who sometimes rolls around in the dirt. (OK, so they all do that all the time, but you take my meaning.)

I'm a big proponent of "say yes," but not when it guts the core feature of an otherwise terrifying monster.

I am not sure that the design of the Xorn extends to avoiding opportunity attacks. Some flying creatures get the Flyby trait which specifically allows them to specifically avoid OA while flying. I don't think Earth Glide states you avoid OA.

As for what I would do, the Xorn is leaving their reach. Reach extends up and down as well. and most characters can't really attack below the ground (or even below their own feet without a reach weapon). I would give A,B, and C opportunity attacks. I feel the Xorn is leaving their reach as he burrows/earth glides into the floor.

 

[Paraxis]

Reach as a game term is 5' for most players, not literal reach. An enemy who moves around a wall but still stays within 5' of them by the book would not provoke an attack of opportunity.

Now if you are talking about leaving reach as in where the character could attack you that is something else, and A, B, and C would get an attack of opportunity. Just be consistent in your rulings.

 

[ranger69]

I have only played the game once so far. However I think that AOO should be adjudicated on a case by case basis using common sense.

Although the Xorn in the example above could possibly have used the disengage action to avoid AOO.

 

[Plaguescarred]

Does character A get an Opportunity Attack on the xorn?

I don't think Character A should get one since he can't see the xorn leaving its reach while 5 feet undergound under Character C.

 

[Skyscraper]

I think none of the PCs should get an OA.

First, the xorn has earth glide. He doesn't burrow. He glides into the earth unimpeded - at least, this is how I understand his power: it has the same "burrow" speed as its base speed, and gliding into earth or stone doesn't cause the earth or stone to be affected. This movement, in itself, and to me, means that he has an ease of movement when moving into the ground. So moving into the ground, in itself, is not something that provokes OAs, no more than normal movement does.

The next question is then whether the xorn moves out of an PC's reach when burrowing straight down.

IMO, when the xorn dives into the ground, he remains within each of the PC's reach. To take the 4E squares system as a reference, imagine that the xorns is in the center of a cube that is 3x3x3 squares (i use the expression "square" here, but it is understood that they're 1x1x1 cubes, to be more precise). Each of the other squares are adjacent to it. The middle layer is ground level, the bottom layer is below ground, and the top layer is above ground and is of no concern to us in this example. The adjacent PCs A, B and C are in the other squares in the middle layer around the xorn. When the xorn dives into the ground, he moves from his center-middle layer square into the underlying one. This underlying square of the bottom layer, is also adjacent to the squares that the PCs occupy, albeit diagonally downwards. He hasn't moved out of any PC's reach, technically. Thereafter, he is "part of" the ground. PCs cannot drive their swords into the ground as a reaction to hit it as it leaves their reach (e.g. PC A), because they can't see it.

Moving downward into a diagonally adjacent square, is the same thing as any creature moving around a PC on ground level, from a facing square to a diagonally adjacent square. This doesn't cause an OA in 5E. I see no difference between the two moves.

I think, as mentioned by JoeLiker above, that this is also what makes this monster interesting and unique. It has a way to move around and pop up at unexpected places.

You can have an encounter with xorn be very creepy and unusual by having him remain underground for some time, before he surfaces to attack PCs by surprise. Each round. With the 5E rule allowing move-attack-move, I don't see why the xorn would do otherwise than hit-and-run, considering this power. To me, this requires the PCs to find ingenious ways to battle this creature. I mean: why even have it surface entirely? If you were a xorn, why move up onto the ground to fight? Remain underground always, and launch attacks from underfoot. (I had a battle with a black dragon in a lake against PCs like that in 4E: the dragon remained submerged at all times, at best it came 10 feet below water level to attack swimming characters in its 10' range.)

Here are some ways I see this encounter running, as the xorn does hit and run tactics from below:

1) The xorn cannot be attacked when it is enterily "within" the ground. Only when he emerges partly to attack with claws and mouth, do the PCs get an attack.
2) If the xorn never surfaces entirely (which I don't see why it should), then it benefits from cover (-2 or -5 or disadvantage depending on how the DM feels) if it is attacked
3) the PCs would probably want to try to find safe havens where the xorn can't earth glide, a bit like in the movies Dune or Tremors with the giant worms. Consider putting some terrain that is not something the xorn can pass through. An island of some sort. Or trees. It'll be fun, once they're on their island/tree, to hear the players discuss in character how they'll get away from this lurking foe...
4) the PCs could ready actions to hit anything that pops up in a given direction. I guess triggers and orientation are key here. I would probably roll randomly, with dice on the table for all to see, to determine where the xorn next hits, and if PC triggers work, then they are able to attack it.
5) perhaps some magic can affect it particularly, even if it's not mentioned in the monster entry? I would certainly welcome original ideas from players. For example, perhaps thunderwave forces it out of the ground entirely. Shocking graps perhaps forces it to remain in its partly ground-protruding position for a round. Etc... Of course, any type of paralysis would be most welcome.
6) perhaps the players can think of something to trick the xorn into attacking at a determined spot to be able to ready actions at that spot? Like thomping on the ground? That sounds neat.

I think this can make for a fun battle with an unusual twist, really.

 

[Dausuul]

Perhaps not. But you don't know that he isn't either (okay, I got lazy in parsing negatives. You know what I mean, I think?).

So the fair way to do it would be to go square-by-square. The first square, A would get his OA.

Why? The xorn is still in reach of A on the first square. That's the square 5 feet straight down from its original position. It's still adjacent to A, B, and C, just covered by rock.

TLDR: You don't decide OAs at the beginning of a creatures movement, only when he would provoke one.

In that case, nobody gets any OAs against the xorn, because by the time it makes a move which would provoke one, it's protected by total cover. Which is what a strict reading of the rules would say, and Joe Liker makes a good case for why that reading is appropriate here.

 

[Thaumaturge]

Why? The xorn is still in reach of A on the first square. That's the square 5 feet straight down from its original position. It's still adjacent to A, B, and C, just covered by rock.

This was my argument, for sure. It's not the xorn's fault they can't attack him in his new square just below them.

Thaumaturge.

 

[Tormyr]

I completely understand where most everyone is coming from, but the difficulty I see with this interpretation is that the only way to fight it is by readying an action (I am looking for the board member whose sig says, "The first sign of a broken rule is when the solution is to ready an action.") At this point, the Xorn could pop up, hit, and descend with relative impunity.

It isn't the end of the world by any means, but it seems like it is close to the only way a level 5 party could combat it.

 

[Boarstorm]

Why? The xorn is still in reach of A on the first square. That's the square 5 feet straight down from its original position. It's still adjacent to A, B, and C, just covered by rock.

In that case, nobody gets any OAs against the xorn, because by the time it makes a move which would provoke one, it's protected by total cover. Which is what a strict reading of the rules would say, and Joe Liker makes a good case for why that reading is appropriate here.

Agreed, actually. I was incorporating the discussion upthread about if A were to be given one (at disadvantage or with cover, etc), and moving forward with it as a given when couching my own arguments.

 

[Paraxis]

OK I am convinced, I still like the say "yes but" approach, but to be consistent character A should not get an attack of opportunity.