Subtle rule changes compared to D&D

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When looking over the Gamma World rules, I noticed a few things that were different from the "parent" D&D rules.

1. You can cross corners of blocking terrain diagonally (the Yexil on the page 21 example apparently didn't get this memo).

2. Forced movement can move a target to a square that the attack doesn't have line of sight or effect to.

3. Creatures don't grant cover against ranged attacks.

4.  You need line of sight to the origin square of an area burst attack you make. 

5. You can only make one opportunity attack on an enemy's turn.

There are of course other differences, like the lack of grab and charge attacks, but these are less obvious, and easy to miss if you're used to the D&D rules. I probably missed a couple of other minor things as well, as I only just sat down with the book. 


4.  You need line of sight to the origin square of an area burst attack you make. 
 


Odd.  That means that someone that's blinded can't make an area burst attack at all.


5. You can only make one opportunity attack on an enemy's turn.
 


How is that different from 4E?  You already only get one opportunity action per other creature's turn, so you never could make more than one OA on a given enemy's turn.
5. You can only make one opportunity attack on an enemy's turn.

Do you mean that the strict, literal GW wording doesn't allow for OA's during an ally's turn? Does that appear intentional?

For that matter: do the others appear intentional? (other than #3, which I believe was intentional)

I have no idea whether these alterations stem from the much briefer rules text in GW, or whether they are intentional.

Concerning the opportunity attacks, D&D allows one opportunity action per creature's turn, while GW allows one per enemy's. As the text actually says, "One for Each Creature's Turn: You can make only one opportunity attack on a given enemy's turn...",  you could plausibly read it either way. Not that you usually need to make opportunity attacks during your allies' turns, though you might due to readied actions.

Actually, readied actions seems to be another things that was cut from GW, and delaying seems to have joined it in extinction.  
3. Creatures don't grant cover against ranged attacks.

5. You can only make one opportunity attack on an enemy's turn. 

Aside from these two, which are both pretty explicit, I think we're just seeing artifacts of the briefer presentation.  I'd certainly still allow a character to throw a grenade into a cloud of smoke or a blinded Hawkoid to Shriek, for instance.

 

 

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"One for Each Creature's Turn: You can make only one opportunity attack on a given enemy's turn...",  you could plausibly read it either way. Not that you usually need to make opportunity attacks during your allies' turns

Ah... then yes, I'd let the original D&D rules that this was duplicating be the deciding factor. The fewer differences the better. The writer made an easy mistake. No biggie. Expecting the GW rules to be perfectly written would not seem recommended.

Do these rules differences matter?

If I post on the local store's message board about starting a GW game or a one-off, I'm likely going to get people who have D&D4E experience.

Do any of these differences actually matter or in any way cause problems if I just ran it with the D&D combat rules? 

Do any of these differences actually matter or in any way cause problems if I just ran it with the D&D combat rules? 



The rules never matter as long as everyone at the table use the same ones. I just think it's interesting to see what changes the writers saw fit to make for this offshoot product. 
I found three more of these changes in the rules.

Coup de Grace is gone, so the helpless condition isn't much more potent than stunned.

You don't recover when you roll 20+ on a death save, you just keep being stable (spotted this one in another thread).

When flying, you don't need to move two squares to stay airborne. Hawkoids rejoice!
I found three more of these changes in the rules.

Coup de Grace is gone, so the helpless condition isn't much more potent than stunned.

You don't recover when you roll 20+ on a death save, you just keep being stable (spotted this one in another thread).

When flying, you don't need to move two squares to stay airborne. Hawkoids rejoice!

fwiw: since the game is called "D&D Gamma World", I reckon that one might have license (i.e. even in an official game) to apply certain applicable D&D rules even if they are not in the GW book.
I found three more of these changes in the rules.

Coup de Grace is gone, so the helpless condition isn't much more potent than stunned.



Helpless is actually much les potent than stunned without CdG, since all it does in GW is make you grant combat advantage.  I don't know that there's anything in the game that causes helpless without causing unconcious, though, so it may not come up.
There isnt in GW, though there is a warlock power in 4E that causes helpless (save ends).
As I mentioned in other threads, technically I don't see any actions called "Charge" or "Crawl" either, but since they are mentioned in the Killing Bite power and Prone condition, respectively, I'm ruling that they exist and work as in DnD.  Just hope some rules gurus at Wizards are reading these and will clarify them in errata.

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1. You can cross corners of blocking terrain diagonally (the Yexil on the page 21 example apparently didn't get this memo).



I'm pretty sure you can not.

The second sentence under "Obstructions and Difficult Terrain" on page 21 reads: "When an object fills a square, you can't move diagonally across the corner of that square unless you teleport." While they don't call it "blocking terrain" by name, their examples match up to the examples of blocking terrain in the Rules Compendium - a wall or large pillar.

I think our friendly mutant in the diagram on page 21 can cut the corners of that car because it doesn't completely fill the space.


The second sentence under "Obstructions and Difficult Terrain" on page 21 reads: "When an object fills a square, you can't move diagonally across the corner of that square unless you teleport."


Ah yes, missed that. I was really wondering about the reason for changing that. All is well, I guess.
4.  You need line of sight to the origin square of an area burst attack you make.  


Odd.  That means that someone that's blinded can't make an area burst attack at all.


Actually, per RAW and not including anything outside the GW rulebook, line of sight doesn't actually require that you be able to see (as long as the imaginary line from your space to the target square doesn't pass through an object or effect that blocks vision, you're good) and the blinded condition doesn't block line of sight.  

Everything still has total concealment of course.

I'd certainly still allow a character to throw a grenade into a cloud of smoke or a blinded Hawkoid to Shriek, for instance.


Obscuring terrain (smoke) doesn't block line of sight (the description states it "may" but it does not unless explicitly stated), and the Hawkoid's Shriek is a close, not an area. 



I'd certainly still allow a character to throw a grenade into a cloud of smoke ...


Obscuring terrain (smoke) doesn't block line of sight (the description states it "may" but it does not unless explicitly stated). 
So you're saying a grenade /would/ bounce off of a completely opaque cloud of smoke (or 'darkness field' or whatever) that explicitly blocks LoS but not LoE?

 

 

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Yep.  Although, why you'd make it explicitly block LOS, as opposed to making it heavily obscured terrain (as is intended), I can't imagine.

"Line of sight" is a sort of common use misnomer that abstracts the ability for a creature to sense another creature.  It is primarily sight-based, but not exclusively.

I'd certainly still allow a character to throw a grenade into a cloud of smoke ...


Obscuring terrain (smoke) doesn't block line of sight (the description states it "may" but it does not unless explicitly stated). 
So, a grenade /would/ bounce off of a completely opaque cloud of smoke that explicitly blocks LoS?


Don't confuse line of sight with line of effect. Two different things. This is one reason why I liked the scatter rules from previous editions of D&D/Gamma World. If you don't have line of sight, the grenade will hit a spot around the target and then bounce to it's final exploding point.

My ruling will be this: If you miss, roll 1d8. Starting in the square closest to you, label each square adjacent to the target 1, 2, 3, ..., and 8 in a clockwise direction(a close burst 1 diagram will show what I'm talking about). The d8 roll dictates the initial landing square. Your character's str/con mod (whichever was used to throw the grenade) is the number of squares the grenade bounces. If the grenade hits a solid surface during it's bounce it reverses direction. Once it moves the required number of spaces, it explodes. You can also rule that if the landing spot is blocked by solid surfaces then it will reverse direction along the path it was thrown as it's bounce move and explode after it moves the modifier distance plus any remaining squares it was moving to it's initial landing spot.

This could get ugly if the grenade bounces off and hits you or your allies...
An addendum for the simultaneous response:

It wouldn't bounce off, per se, it just wouldn't be an eligible origin square.  But I can't imagine a situation in which, in game terms, an intangible, obscured square would need to be ruled as blocking line of sight.
Ironically, while you guys were both simultaneously responding, I was simultaneously editing.  ;)
An addendum for the simultaneous response:

It wouldn't bounce off, per se, it just wouldn't be an eligible origin square.  But I can't imagine a situation in which, in game terms, an intangible, obscured square would need to be ruled as blocking line of sight.

So, if you can't imagine something blocking LoS without also blocking LoE, what's the point of the distinction in the first place?

 

 

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An addendum for the simultaneous response:

It wouldn't bounce off, per se, it just wouldn't be an eligible origin square.  But I can't imagine a situation in which, in game terms, an intangible, obscured square would need to be ruled as blocking line of sight.

If you can't see through it (obscured) you lose line of sight to anything behind it. Intangibility means that things can pass through it. So a grenade could pass through a pillar of dense, black smoke but you'd suffer the standard penalties for something with complete concealment.

If you didn't hit the target, chances are that the grenade won't disintegrate into nothingness (though for simplicity's sake that works). Adding scatter and bounce rules for grenades brings some slight realism to the game and might make it more fun. At least I think it'd be fun to add a little chaos from a missed grenade bouncing around a battlefield
So, if you can't imagine something blocking LoS without also blocking LoE, what's the point of the distinction in the first place?

Line of Effect and Line of Sight are two completely different things. If someone is behind an invisible forcefield, you have line of sight but you do not have line of effect. If someone is behind a wall that doesn't fully cover the blast radius of an area or blast, you don't have line of sight, but you do have line of effect.

If someone is standing behind dark, black, obscuring smoke, you don't have line of sight but you have line of effect (due to intagilbility of the smoke).