The description of the Melf’s Minute Meteors spell states, in part:
[…] you can expend one or two of the meteors, sending them streaking toward a point or points you choose within 120 feet of you. Once a meteor reaches its destination or impacts against a solid surface, the meteor explodes. Each creature within 5 feet of the point where the meteor explodes must make a Dexterity saving throw. […]
This seems like a fairly easy ruling for when choosing a point, choose a point in between four squares and any creature in those four squares need to make a saving throw like so:
However, how does this interact if if impacts a singular creature in the middle of a square? Does only that creature make it because only that creature is fully within 5 feet, or do the creatures in the 8 surrounding squares also need to make it (reference pics below)?
Area of effect is centered on an intersection (when on a grid)
The meteors target a point and then explode in a radius – they thus have an area of effect.
When using a tactical map rules variant with area of effect spells, you should select an intersection, not the center of a space.
DMG 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 that square.