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.
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?