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View Full Version : PotA Spells Earth Tremor and Ice knife questions.



Rhaegar
2015-11-29, 08:50 PM
I'm currently running a princes of the apocalypse campaign. I'm a first time DM a couple months into the campaign, and all the players are first time to D&D outside of video games, though we did previously do a GURPS campaign with one of the current players DMing that. We're having some questions about two campaign specific spells. We're playing on 5ft grid maps. The debate is which grid areas would be affected by the spells. I'm looking for both RAW responses, as well as how you might house rule them outside of RAW. Our group includes players with masters degrees in Physics, Math, and Aerospace engineering, so we are a highly technical group.

The first spell up for debate in the party is Earth Tremor: Range: Self(10 foot radius) You cause a tremor in the ground in a 10-foot radius. Each creature other than you in that area must make a Dexterity saving throw. On a failed save, a creature takes 1d6 blugeoning damage and is knocked prone. If the ground in that area is loose earth or stone, it becomes difficult terrain until cleared. When you cast this spell using a spell slot of 2nd level or higher, the damage increases by 1d6 for each slot level above first.

My players are arguing for it to cover:
http://imgur.com/FXAzwT2
They argue that it would cover 21 boxes around the caster, the 3x3 box surrounding the caster, and the additional 3 boxes further out. They're argument is that the spell originates from the caster, and using movement rules from the casters box using alternating 5ft/10ft diagonal movement. This is how far you could move 10 feet, so the spell should be able to reach those boxes. Argument 2, if I can attack the square with a 10foot reach weapon, a 10ft radius spell should also be able to hit it.

Counter arguments. 1. A 10ft radius circle has an area of 314 ft^2, What they want would be 525 ft^2. There are seperate rules for movement, melee weapons, ranged weapons and spells. We need to stick to the rules for spells. Also to attack with a melee weapon you aren't just standing in the center of the square you would step and attack towards the opponent, attacking more from an edge or a corner of the box the caster is in.

DM Option 1:
http://imgur.com/X1YXynM
Going Strictly rules as written of the DM guide 251, choose an intersection of squares or hexes as the point of origin of an area of effect, then follow its rules as normal, If an area of effect is circular and covers at least half a square it affects the square. Here you have the standard 10foot radius circle centered on a cross hair with 12 squares covering 300 ft^2 of surface, where a pure circle is 314^ft. Argument against is that the origin is the caster, and it should be centered on the caster. With this you also negate one corner surrounding the caster which doesn't seem appropriate if the caster is the origin.

DM Option 2:
http://imgur.com/E9FrQH7
If you go by specific beats general, and the origin is the caster, not a point in space, and the caster is at the center of the square, any square over 50% is affected, but less than 50% is not affected you would end up with only 9 squares covered. Here you only end up with 225^ft compared to a 314ft^2 pure circle. The centered edge squared while close are less than 50%

Not yet proposed Option 3:
http://imgur.com/ejkT5dP
The average person is 18 inches wide. If the origin is a person, and it is 10feet from the caster, the radius may end up being a circle with an 11 foot radius. An 11 foot radius centered at the center of a square would end up with 13 squares and 325 ft^2 of coverage just slightly over 314 ft^2 of a natural circle. This option seems like it might be most acceptable to the party as a whole.

How would you rule the effects of this spell?


The next spell in question is Ice Knife: You create a shard of ice and fling it at one creature within range. Make a ranged spell attack against the target. On a hit, the target takes 1d10 piercing damage. Hit or miss, the shard then explodes. The target and each creature within 5 feet of the point where the ice exploded must succeed on a Dexterity saving through or take 2d6 damage. When you cast this spell using a spell slot of 2nd level or higher, the cold damage increases by 1d6 for each slot above 1st

The question: Does the AoE effect cover 4 squares or 9 squares.
http://imgur.com/QPy7LZ7
http://imgur.com/t5ZxGdW
My players are arguing that it explodes in the center and hits 9 total squares, the square the caster is in, and all adjacent squares. The thing i'm worried about is that it is a 5ft explosion, which is 78.54 ft^2 for a natural circle. 9 squares is 225 ft^2 more than double 4 squares which is 100 ft^2, and nearly triple the size of a natural 5ft radius circle.

The players argue that the 9 squares is appropriate as all 9 squares are within ft of the target. Counter argument is that the explosion is specifically 5ft from the point where the ice exploded, the ice wouldn't explode in the center of the person, they may have leaned forward to catch it with a shield, or it may have exploded right on their body in front of them. And if it hit them and exploded, their body would naturally block the explosion from hitting squares behind the player. But while we might know where it explodes if it actually hits it's target where would it explode if it missed. If it explodes on a crosshair, but misses, would it explode on any random crosshair surrounding the player, or would it still explode on the crosshair nearest to being between caster and target.

This spell unlike earth tremor has a single point as it's origin of the ice knife exploding, and isn't actually originating from the person, but a point of explosion.

How would you, or how have you handled these two spells at your tables. Ultimately how are these spells balanced. If ice knife for instance is actually balanced around 9 squares I don't want to nerf it, but if it's balanced around 4 squares, but I let it affect 9 squares it becomes quite powerful by comparison.

Safety Sword
2015-11-29, 09:25 PM
I think I can "fix" this for you.

You actually take up a 5 ft space. So, just count two squares away and that's your 10 ft. radius. Ignore Pythagoras with respect to diagonals. Just count from your square. Anything that takes two counts to get to is in the radius.

Seriously, just make it as simple as possible and move on with the game. On a grid there are no circles. Just break the radii into 5 ft lengths and count. I find it better to sacrifice precision with measurements for speed and simplicity.

Works even better on a hex map, by the way.

RedMage125
2015-11-29, 09:26 PM
You go by intersection, for all AoEs. You even quoted the DMG page number.

If you are using Battlemats/Grids, you can buy (or make) wire frame templates for many AoEs. I still have some from 3.xe that work for 5e (4e was different).

So Earth Tremor is a grand total of 12 squares. 10 feet from the intersection. Option 1 is correct.

Similarly, Ice Knife would be 4 squares. The initial target is affected, and one of the target's space's corners is now the point of origin for a 5 foot burst, which affects the 4 squares touching that corner.

People who use theatre of the mind, or use minis somewhat but do not use tactical grids may have different mileage from AoE spells, as the curve actually matters. But for using grids, all AoE radii look like 8-bit "circles" of various sizes.

What your players are suggesting is how 4e AoEs worked. Scorching Burst, for example, was an At-Will Wizard power that read "Area Burst 1 within 10". Under that system you targeted a SQUARE (within 10 squares of the caster), and then had a "burst" of one square out in each direction, giving you a 3x3 area. So 9 squares total were affected. This was considered a low-level AoE. A Burst 2, similarly chose one square as the center, and went out 2 squares in all directions (including diagonally), giving you a 5x5 area. Close Blasts were also square shaped in that edition, instead of cones, which all other editions used. Burning Hands, for example, was a "Close Blast 3", which meant that it was a 3x3 square that had to have one side or one corner touching the square of the origin (in this case the caster, since the range was "Close"). 4e was designed from the ground up to be used with battle grids, however, even PHB races listed their speed in number of squares moved.

Pre-4e and 5e AoEs use things like "cylinders", "cones" and "circles/spheres". When you use a grid system, there are tactical advantages (for example, knowing exactly where monsters are relevant to your characters and having precise placement of AoEs. The tradeoff is the area "lost" with circular AoEs.

Vogonjeltz
2015-12-01, 05:58 PM
The first spell up for debate in the party is Earth Tremor: Range: Self(10 foot radius) You cause a tremor in the ground in a 10-foot radius. Each creature other than you in that area must make a Dexterity saving throw. On a failed save, a creature takes 1d6 blugeoning damage and is knocked prone. If the ground in that area is loose earth or stone, it becomes difficult terrain until cleared. When you cast this spell using a spell slot of 2nd level or higher, the damage increases by 1d6 for each slot level above first.

My players are arguing for it to cover:
Apparently I can't post images since this is my first post.
imgur dot com / FXAzwT2
They argue that it would cover 21 boxes around the caster, the 3x3 box surrounding the caster, and the additional 3 boxes further out. They're argument is that the spell originates from the caster, and using movement rules from the casters box using alternating 5ft/10ft diagonal movement. This is how far you could move 10 feet, so the spell should be able to reach those boxes. Argument 2, if I can attack the square with a 10foot reach weapon, a 10ft radius spell should also be able to hit it.

The rules for a sphere aoe are on page 205 of the PHB. The rules for playing on a grid and determining ranges is found in the PHB on page 192.

Get a compass and set it to a length of 2 cubes (10 feet), then place the center on the characte (the center of their cube) and draw a circle. If it's included in the circle, at all, it's in the aoe.

Functionally this is what the players have suggested, you count the adjacent square + any square touching them (that's 10 feet out).



The next spell in question is Ice Knife: You create a shard of ice and fling it at one creature within range. Make a ranged spell attack against the target. On a hit, the target takes 1d10 piercing damage. Hit or miss, the shard then explodes. The target and each creature within 5 feet of the point where the ice exploded must succeed on a Dexterity saving through or take 2d6 damage. When you cast this spell using a spell slot of 2nd level or higher, the cold damage increases by 1d6 for each slot above 1st

The question: Does the AoE effect cover 4 squares or 9 squares.

9 squares, that's how the rules on grids work. A diagonal square is still only 5 feet distant as the crow flies.


You go by intersection, for all AoEs. You even quoted the DMG page number.

This is not true in the case of aoe that has a range of self. Those originate from the character's square, not an intersection.

RedMage125
2015-12-01, 08:02 PM
This is not true in the case of aoe that has a range of self. Those originate from the character's square, not an intersection.

You have a page number to cite your source on that? Because it goes against everything I've ever done.

Vogonjeltz
2015-12-02, 06:58 PM
You have a page number to cite your source on that? Because it goes against everything I've ever done.

Yes, Page 202, Range: "Spells that create cones or lines of effect that originate from you also have a range of self, indicating that the origin point of the spell's effect must be you (see "Areas of Effect" later in the this chapter)." [sic]

Page 204, Areas of Effect: "Every area of effect has a point of origin, a location from which the spell's energy erupts. The rules for each shape specify how you position its point of origin. Typically a point of origin is a point in space, but some spells have an area whose origin is a creature or an object."

If this makes you pause and be like 'Wouldn't that harm the caster?', we then refer to the various shapes:

Page 204, Cone: "A cone's point of origin is not included in the cone's area of effect, unless you decide otherwise."
Page 204, Cube: "A cube's point of origin is not included in the cube's area of effect, unless you decide otherwise."
Page 204, Cylinder: "A cylinder's point of origin is included in the cylinder's area of effect."
Page 205, Line: "A line's point of origin is not included in the line's area of effect, unless you decide otherwise."
Page 205, Sphere: "A sphere's point of origin is included in the sphere's area of effect."

A sample of spell's that have a shape and range of self:
Antilife Shell (see antimagic field), Antimagic Field (specifies that the sphere is centered on the caster and moves with them), Arms of Hadar, Aura of Life, Aura of Purity, Aura of Vitality, Burning Hands (cone), Circle of Power, Color Spray, Cone of Cold, Conjure Barrage, Control Weather, Destructive Wave, Globe of Invulnerability, Gust of Wind, Leomund's Tiny Hut, Lightning Bolt, Prismatic Spray, Speak with Plants, Spirit Guardians, Sunbeam, Thunderwave

Picking a vertex is just fine for non-self aoe, such as Fireball.

Rhaegar
2015-12-02, 10:01 PM
The point of origin is the player, yes. But the player isn't necessarily perfectly in the center of the square. The square is just the best representation of where the character is within the pixel size of a 5 foot grid. The main thought process for me in having it cast at a crosshair near the caster is that they are are more towards that corner of their box. Also on a cross hair you get 12 boxes which roughly represents 95% of what a pure 10yd radius circle would be, where as 9 boxes only accounts for 72% of the pure circle. Ultimately I'd probably allow any person casting the spell to take either option, whatever they thought gave the best results.

georgie_leech
2015-12-02, 10:11 PM
Simplest option is the one that 4e went with, all circles and spheres are actually squares for the purposes of targeting because calculating diagonals is a pain for not much benefit. If you want a more rigorous approach, consider cutting out templates for your areas that match the scaled dimensions, and center them wherever the effect is originating from. If a square falls under any part of that, it's in the area, even if it's mostly outside it, because otherwise you just end up a series of ever smaller squares with an arbitrary cutoff point; why not just use the default space?

RedMage125
2015-12-02, 10:20 PM
Simplest option is the one that 4e went with, all circles and spheres are actually squares for the purposes of targeting because calculating diagonals is a pain for not much benefit. If you want a more rigorous approach, consider cutting out templates for your areas that match the scaled dimensions, and center them wherever the effect is originating from. If a square falls under any part of that, it's in the area, even if it's mostly outside it, because otherwise you just end up a series of ever smaller squares with an arbitrary cutoff point; why not just use the default space?

I have a set of wire frames for use with a battle grid that has 15', 30' and 60' cones, as well as another set with 10', 20' and 60' radii. They're awesome.

georgie_leech
2015-12-02, 10:27 PM
I have a set of wire frames for use with a battle grid that has 15', 30' and 60' cones, as well as another set with 10', 20' and 60' radii. They're awesome.

Ooh, those would be handy. No more moving minis or whatever random bits I'm using to represent stuff, just putting the frame down around the center. Are there any guides on them to help you find the centers on the circles?

RedMage125
2015-12-02, 11:55 PM
Ooh, those would be handy. No more moving minis or whatever random bits I'm using to represent stuff, just putting the frame down around the center. Are there any guides on them to help you find the centers on the circles?

No, they are empty wire frames. I find my center point, count the number of squares out to one end, and set the wire frame down there, starting with that side. If I don't like where it falls, I just move it from there.

Safety Sword
2015-12-03, 12:07 AM
No, they are empty wire frames. I find my center point, count the number of squares out to one end, and set the wire frame down there, starting with that side. If I don't like where it falls, I just move it from there.

you can do a similar thing with cardboard areas cut out, that's what my group likes.

Vogonjeltz
2015-12-03, 06:27 PM
The point of origin is the player, yes. But the player isn't necessarily perfectly in the center of the square. The square is just the best representation of where the character is within the pixel size of a 5 foot grid. The main thought process for me in having it cast at a crosshair near the caster is that they are are more towards that corner of their box. Also on a cross hair you get 12 boxes which roughly represents 95% of what a pure 10yd radius circle would be, where as 9 boxes only accounts for 72% of the pure circle. Ultimately I'd probably allow any person casting the spell to take either option, whatever they thought gave the best results.

The game deliberately makes sacrifices of fidelity in the name of function (see: Diagonal movement when using the Grid Variant in the textbox on page 192).

Ranges on a grid are also determined loosely. "Ranges. To determine the range on a grid between two things-whether creatures or objects-start counting squares from a square adjacent to one of them and stop counting in the space of the other one. Count by the shortest route."

So it doesn't matter that the character might be anywhere within the 5 foot space, the range is effectively rounded off at 5 feet. If using a grid, someone in an adjacent square is 5 feet away.

Spells aren't in yards, but as I said, if we're talking spheres then as long as it doesn't have a range of self, you would pick a vertex.

If it were self, then it originates on that square, and you would count out 30 feet (10 yards) from the center of that square, according to the rules, so long as 1/2 of any other square is within the area of the circle, then it would be affected. So if you use a compass, or a piece of string, or a precut circle of the appropriate size (there are many potential sizes, so I'd recommend the compass or string) then you can easily see if the circle cuts across +50% of a square. (I would point out that in this case a spherical aoe with range of self and 10 foot radius hits 13 squares (including the origin), whereas one placed at a vertex would only affect 12 squares). So there is a difference.

Rhaegar
2015-12-03, 07:11 PM
(I would point out that in this case a spherical aoe with range of self and 10 foot radius hits 13 squares (including the origin), whereas one placed at a vertex would only affect 12 squares). So there is a difference.

How do you come to 13 squares. If the origin is a point in the center of a square and you draw a perfect 10 yard radius circle. While the circle reaches the center of the 4 squares directly in straight lines, the nature of the curve means it reaches less than 50% of that square. It only becomes 13 squares if the radius becomes slightly larger than 10yards. If you make a circular radius 10.5 or 11 yards it would become 13 squares. My potential argument for 13 squares being that it could be 10yards from the edge of the caster, making it about a 11 yard radius or 13 squares. But a perfect 10 yard radius circle from the center of a square is only 9 squares, if you go by a pure greater than 50% less than 50% rule.

Safety Sword
2015-12-03, 08:01 PM
How do you come to 13 squares. If the origin is a point in the center of a square and you draw a perfect 10 yard radius circle. While the circle reaches the center of the 4 squares directly in straight lines, the nature of the curve means it reaches less than 50% of that square. It only becomes 13 squares if the radius becomes slightly larger than 10yards. If you make a circular radius 10.5 or 11 yards it would become 13 squares. My potential argument for 13 squares being that it could be 10yards from the edge of the caster, making it about a 11 yard radius or 13 squares. But a perfect 10 yard radius circle from the center of a square is only 9 squares, if you go by a pure greater than 50% less than 50% rule.

You guys are doing my head in.

Just measure from the edge of the square of the caster and count any square it touches.

Over-thinking it is bad. K.I.S.S.

Vogonjeltz
2015-12-05, 03:47 AM
How do you come to 13 squares. If the origin is a point in the center of a square and you draw a perfect 10 yard radius circle. While the circle reaches the center of the 4 squares directly in straight lines, the nature of the curve means it reaches less than 50% of that square. It only becomes 13 squares if the radius becomes slightly larger than 10yards. If you make a circular radius 10.5 or 11 yards it would become 13 squares. My potential argument for 13 squares being that it could be 10yards from the edge of the caster, making it about a 11 yard radius or 13 squares. But a perfect 10 yard radius circle from the center of a square is only 9 squares, if you go by a pure greater than 50% less than 50% rule.

Hrm, you're right, I was just treating it as being half the square if it hit the 50% mark (to the middle of the square), but the curve would make it slightly less than 50% of the total square area.