I've always played that if you were to cast an AOE spell and it was to touch 1 square of the large, huge or gargantuan creature it would take the damage/be affected. However, talking to another DM today he is a lot more old school and has played with Miniatures a long while. He states the rule is that 50% of the creature must be in the AOE or it does not damage/affect the creature.
I have spent the last few hours doing research to no avail. Sure I see the rules in regards to if an AOE affects a square DMG pg 251: "Choose an intersection of squares or hexes as the point of origin of an area of effect ... If an area of effect is circular and covers at least half a square, it affects that square."
So from this we know if a 5' square is actually affected by the spell. But we do not yet know if the spell damages/affects said creature.
For example; A Gargantuan creature takes up 16 squares in total(4x4 squares). So if the fireball touched just 1 of those 16 squares IMHO the creature would then take said damage. However, no where in the PHB nor the DMG that I'm seeing states how much of a creature must be in an AOE for it to affect said monster. Afterall a Gargantuan creature does occupy a 4x4 grid it really is probably only 2x2-3x3 but moving around inside said grid so it could possible not be affected using that logic.
Lastly: in DMG pg. 249 it states: Many spells and other game features create areas of effect, such as the cone and the sphere. If you're not using miniatures or another visual aid, it can sometimes be difficult to determine who's in an area of effect and who isn't. The easiest way to address such uncertainty is to go with your gut and make a call."
This to me says hey we don't have a rule it's up to the DM to decide if an AOE hits a monster even though you might use something like roll20 or Foundry and can see if it touches one of the squares the monster occupies.
Once again, just looking to see if there is any actual Sage Advice(can't find any) or actual rules clarifying this in an official core book.
The rules given in the PHB and DMG leave it up to the DM to decide if a creature is affected or not when only some of the squares it occupies are affected by an area of effect.
In short, when using a template for an AoE in gridded combat any square is even partially shaded by the template is affected by an AoE. If a creature's miniature is in an affected square then the creature is affected.
a creature is included in an area of effect if any part of the miniature’s base is overlapped by the template.
This can be easily extrapolated to mean that if any one square out of the 16 squares that a gargantuan creature occupies is affected by the AOE then the creature is indeed affected.
If instead we are only using the PHB and DMG and decide that it's basically the DM's call then I would say that a reasonable compromise might be that if at least one square but less than 50% of the squares occupied by the creature is affected then the creature gets advantage on the saving throw.
I've always played that if you were to cast an AOE spell and it was to touch 1 square of the large, huge or gargantuan creature it would take the damage/be affected. However, talking to another DM today he is a lot more old school and has played with Miniatures a long while. He states the rule is that 50% of the creature must be in the AOE or it does not damage/affect the creature.
I have spent the last few hours doing research to no avail. Sure I see the rules in regards to if an AOE affects a square DMG pg 251:
"Choose an intersection of squares or hexes as the point of origin of an area of effect ... If an area of effect is circular and covers at least half a square, it affects that square."
So from this we know if a 5' square is actually affected by the spell. But we do not yet know if the spell damages/affects said creature.
For example; A Gargantuan creature takes up 16 squares in total(4x4 squares). So if the fireball touched just 1 of those 16 squares IMHO the creature would then take said damage. However, no where in the PHB nor the DMG that I'm seeing states how much of a creature must be in an AOE for it to affect said monster. Afterall a Gargantuan creature does occupy a 4x4 grid it really is probably only 2x2-3x3 but moving around inside said grid so it could possible not be affected using that logic.
Lastly: in DMG pg. 249 it states: Many spells and other game features create areas of effect, such as the cone and the sphere. If you're not using miniatures or another visual aid, it can sometimes be difficult to determine who's in an area of effect and who isn't. The easiest way to address such uncertainty is to go with your gut and make a call."
This to me says hey we don't have a rule it's up to the DM to decide if an AOE hits a monster even though you might use something like roll20 or Foundry and can see if it touches one of the squares the monster occupies.
Once again, just looking to see if there is any actual Sage Advice(can't find any) or actual rules clarifying this in an official core book.
Thanks again for any and all help!
The rules given in the PHB and DMG leave it up to the DM to decide if a creature is affected or not when only some of the squares it occupies are affected by an area of effect.
Xanathar's Guide to Everything give some additional guidance when it describes the Template method for handling AoE's: https://www.dndbeyond.com/sources/xgte/dungeon-masters-tools#TemplateMethod
In short, when using a template for an AoE in gridded combat any square is even partially shaded by the template is affected by an AoE. If a creature's miniature is in an affected square then the creature is affected.
Also in Xanathar's it says:
This can be easily extrapolated to mean that if any one square out of the 16 squares that a gargantuan creature occupies is affected by the AOE then the creature is indeed affected.
If instead we are only using the PHB and DMG and decide that it's basically the DM's call then I would say that a reasonable compromise might be that if at least one square but less than 50% of the squares occupied by the creature is affected then the creature gets advantage on the saving throw.