In the rules for the prone condition, it states:
An attack roll against the [prone] creature has advantage if the attacker is within 5 feet of the creature. Otherwise, the attack roll has disadvantage (PHB 292).
If a wyvern (for example) is 10 feet away from a prone target and makes a bite attack (+7, reach 10 ft., one target (MM303)) would it get disadvantage on the attack because it's body is not within 5 feet of the prone creature, or would the fact that it's head (with all the pointy teeth thingies) is necessarily within 5' give it advantage?
It appears to me that the RAI are meant to give ranged attacks disadvantage against prone targets (logical), but it doesn't make sense for me that disadvantage should also apply to melee attacks with reach beyond 5 feet. I could see reach attacks versus prone targets perhaps being considered as normal attacks. Has anyone seen any discussion of this issue in any of the official channels?
(Please don't answer with "A DM can rule however s/he wants" – I am well aware of this fact and don't find these types of responses terribly helpful. I'll likely end up adding "house rules" to the prone condition to fit my idea of what makes sense, but I'm interested in hearing some informed opinions before I do. Thanks!)
Best Answer
Yes, the Wyvern is probably intended to have disadvantage.
While Word of God could always overturn this (but it didn't), it seems pretty clear that the intent is for this to apply to reach attacks. They have the key phrase "ranged attack" and use it elsewhere in the rules (e.g. in the Monk's deflect arrows ability). This heavily implies that the more awkward wording is there for a reason.
They might have worded it this way so that ranged attacks made from melee are normal, rather than disadvantaged. But I suspect this case is less likely than the reach attack one (your mileage may vary).
In other words, it's not a case where it looks like they used simple language and forgot about some corner cases, like the interaction between druids and lethal damage.
As to why this would be the case, consider that a large wyvern doesn't have a 10' body with a long head that sits 10' away. The entire wyvern occupies a 10'x10' space, and stretches or pounces when it needs to attack outside of reach. This kind of stretching / pouncing will inherently limit the creature's attack vectors, perhaps in a way that dropping to the ground will help.
In other words, the monster isn't right there. The monster is still 10' away.
Also remember that the monster doesn't have to stay at range. As soon as they drop prone, it can close to within 5' and start taking advantage on its attacks.
From a mechanical standpoint, this makes prone a general strategy to take for things attacking you that you can't reach and/or luring things into melee. This simplifies the mechanical design, and helps avoid loopholes.
As a house rule, you can certainly scale down the effectiveness of the prone condition. It's unlikely to break much with the current corpus of monsters. However, doing so will always compete with simply closing to melee and gaining advantage... And it is unlikely that this will be brought into the official rules (although maybe it will! Sloppy templating, etc.).