If my Firbolg lifts a barrel over their head while appearing 3ft taller from their Disguise Self, where does the barrel appear?

Question

Let's say they are 7ft 4in tall, and cast their innate Disguise Self, using the rules from Mordenkainen's Monsters of the Multiverse:

Firbolg Magic • MotM, pg. 15
Once per long rest, you can cast detect magic and disguise self. When you use this version of disguise self, you can seem up to 3 ft. shorter or taller. You can also cast these spells using any spell slots you have. Your spellcasting modifier is either Intelligence, Wisdom, or Charisma (choose when you select this race).

That means they may appear to be 10ft 4in, and then after the spell is cast they decide to lift a barrel above their head (e.g. the barrel is not a 'belonging on your person' when the spell is cast). That means the hands are ~15ft foot above them (~10ft + half height for arms), but the barrel is more like ~10ft above them (~7ft + half height for the arms).

Normally I couldn't see this being an issue for a shorter character, especially as normally the Disguise Self spell only makes you taller/shorter by 1ft:

You make yourself--including your clothing, armor, weapons, and other belongings on your person--look different until the spell ends or until you use your action to dismiss it. You can seem 1 foot shorter or taller and can appear thin, fat, or in between. [...]

So for a shorter character the discrepancy wouldn't be that great. At worst, maybe 10½ft, (if a 6ft character gained 1ft, and lifted the barrel up an extra 3½ft up), vs 9ft (6ft+3ft), which is probably smaller than the object being lifted... so I can imagine being the illusion covers up this up. But even if the barrel is ~3ft in diameter, there is too much to 'cover up' without the spell doing more than it says it does and either the barrel ends up floating between their arms or invisible if it is supposed to appear 2-5ft higher up than it is.

How should I align the rules and my intuition/limited suspension of disbelief on this set up? Or is this a case by case GM problem?

Answer 1

It appears in their hands; that's what the spell does

The spell explicitly describes which senses it can and cannot fool; it fools sight, but not touch:

The changes wrought by this spell fail to hold up to physical inspection. For example, if you use this spell to add a hat to your outfit, objects pass through the hat, and anyone who touches it would feel nothing or would feel your head and hair. If you use this spell to appear thinner than you are, the hand of someone who reaches out to touch you would bump into you while it was seemingly still in midair.

The disguise self spell has a duration of one hour and is not limited by concentration. During that entire time, the disguised person is going to be interacting with their environment. In order to complete its function of disguise and deception, the spell has to be able to fool the sense of sight of onlookers, not just as to what they see on the disguised person, but in the local environment around them.

If I make myself appear shorter, and then reach to open a door, would the door appear to open before my illusory hand touches it? If I make myself appear taller and sit down to sup, would my illusory hand appear to pass through the salt cellar that is too far away for me to actually reach? If I use the spell to appear thinner, but then don a real cloak, would the cloak appear to be suspended away from my illusory body because it lays against the contours of my actual body?

No, no to all of these hypotheticals, because the spell specifies that it can only be detected by touch. It will automatically adjust appearances as necessary to fool visual inspection. The magic keeps the interactions of the target with the world looking believable. If my size-altered firbolg picks up a barrel after the spell is cast, the barrel will appear to be in their apparent hands, regardless of its actual location.

This is, after all, specifically what illusion school spells do; they fool the senses of even careful observers. Illusion is (PHB 118):

magic that dazzles the senses, befuddles the mind, and tricks even the wisest folk. Your magic is subtle, but the illusions crafted by your keen mind make the impossible seem real.

It is impossible for a 7' tall firbolg to lift the barrel 15' over its head. But the magic of the spell makes it seem like that is really the location of the barrel, at least to sight. Only touching the firbolg, the actual barrel, or where the barrel appears to be will reveal the deception.

Answer 2

Floating between their arms

Following the rule of "spells do what they say they do and nothing more", Disguise Self does not change the appearance of carried items.

The spell mentions worn items (emphasis mine):

You make yourself--including your clothing, armor, weapons, and other belongings on your person--look different until the spell ends or until you use your action to dismiss it.

It does not mention carried items, so carried items are not under the effect of the illusion.

Limited suspension of disbelief

I suggest two approaches to marry this rule with your intuition.

The first option is that you follow the rules to the letter. In this case, the creature that cast Disguise Self messed up and forgot that the illusion magic does not work on carried items. It is unaware that other creatures see the barrel floating in the air. This could lead to some hilarious situations.

The second option is that you (and your GM) decide it is more fun if the illusion magic also applies to the barrel. If you go this route, you can play with the "physical inspection" clause of the spell:

[...] The changes wrought by this spell fail to hold up to physical inspection. For example, if you use this spell to add a hat to your outfit, objects pass through the hat, and anyone who touches it would feel nothing or would feel your head and hair. If you use this spell to appear thinner than you are, the hand of someone who reaches out to touch you would bump into you while it was seemingly still in midair. [...]