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I was looking at wall of fire and realized I wasn't sure how to represent the ringed version when on a grid. The spell states (emphasis mine):

You create a wall of fire on a solid surface within range. You can make the wall up to 60 feet long, 20 feet high, and 1 foot thick, or a ringed wall up to 20 feet in diameter, 20 feet high, and 1 foot thick [...]

So assuming we maximize the diameter to 20 feet and use the following rule for areas of effect on a grid from the Dungeon Master's Guide (page 251), we get the following images with the second showing the outer squares, where the ring actually is:

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 that square.

Ringed Wall of Fire Ring Wall of Fire, Edges

However, this image seems incorrect; one could simply leave the ring by moving diagonally, avoiding taking damage entirely. Have I made a mistake in my drawings or is this just a case that the rule happens to not work well with?

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  • \$\begingroup\$ I don’t understand - how could a creature move from inside the circle to outside the circle without crossing it? You’re not talking about burrowing or flying over it. So if a creature is in the middle 4 squares and moves diagonally, it has clearly gone from inside to outside. How are you imagining that it would avoid damage? \$\endgroup\$ – Ira Mar 13 at 4:45
  • \$\begingroup\$ @Ira Because, very technically, the spell does damage when entering the wall. And going diagonally a character never actually touches any red (affected) squares. I agree that physically/real-world they go through the wall but in terms of how the grid-rules work out it seems to make a problem \$\endgroup\$ – Medix2 Mar 13 at 7:17
  • \$\begingroup\$ Looking more closely at your image, what did you intend the dashed red lines to represent? If you see my answer below, I’ll be curious to see what you think! :) \$\endgroup\$ – Ira Mar 14 at 14:33
  • \$\begingroup\$ @Ira Oh that would be me forgetting to make the graph boundary invisible or solid... So you can just ignore the dashed lines, I care about the circle and red squares \$\endgroup\$ – Medix2 Mar 14 at 14:36
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You may want to use an alternative method from XGtE.

Your image is correct, and you cite all relevant rules. The Grid as a visual aid (DMG 250) is different from what the theatre of mind approach offers and provides different results, but there are other methods to adjudicate areas of effect on a Grid.

Xanathar's Guide to Everything's section about Spellcasting gives insight into this in its subsection about Areas of Effect on a Grid (XGtE 86-88). It offers two alternative options, the Template Method (XGtE 86-87) and the Token Method (XGtE 87-88) which offer different results, so you may choose one. From the Token Method:

Circles. [...] a circular area of effect becomes square in it, whether the area is a sphere, cylinder, or radius. For instance, the 10-foot radius of flame strike, which has a diameter of 20 feet, is expressed as a square that is 20 feet on a side, as shown in diagram 2.3.

You can find diagram 2.3. on page 86.

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    \$\begingroup\$ I personally use the Template method and find it very easy to quickly identify what is or isn't affected, and I find that my player's almost never argue about what is or isn't included in an AoE, since it's quite easy to corroborate. If a mini's base is approximately bifurcated by the edge of an effect's template, I include it as being affected by that effect. Sometimes I'm a little more lenient, depending on the situation. The only downside to this method is the need to create additional materials in order to be able to measure out these areas. +1 for a great alternative \$\endgroup\$ – G. Moylan Mar 12 at 22:02
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I'd offer an alternative interpretation, based on circle area of effects - rather than treating the ring of fire as, well, a ring of fire, treat it as a filled circle which is the "interior" (and this circle would be a full 4x4 square with the corners removed), and the "exterior", which is everything else. A creature trying to pass from one to the other must cross the wall. A creature stopping on one of the highlighted squares touches the wall.

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It's effectively a plus shape, enclosing 12 squares.

Ringed Wall of Fire

Your original image shows 4 white squares in the center. While creatures in those squares don't need to make a DEX save when the spell is cast because they aren't literally touching the wall, they are still inside the ringed Wall of Fire (obviously).

The 4 white outer corner squares are outside the ring, because of the 50% rule.

Therefore, if a creature starts in one of the inner 4 squares (inside the ring) and moves diagonally to one of the outer 4 squares (outside the ring), it has definitely crossed the boundary.

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  • \$\begingroup\$ This answer makes sense (honestly I think the spell isn't particularly well written) but know that it does make the selecting a damaging side of the wall a bit odd. If you choose the "in"-side, nothing changes, and if you choose the "out"-side it's another shape as well. The spell just seems weird, and mostly assuming you make a line wall and not a circle (you've got my +1 btw) \$\endgroup\$ – Medix2 Mar 14 at 21:18

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