What spells can an Instrument of the Bards actually impose disadvantage on?

Question

In light of the revelation that an Instrument of the Bards requires a spell with a material component to be used, what spells can it actually be used on?

Answer 1

The November 2018 DMG errata replaces the last paragraph of the old description with:

You can play the instrument while casting a spell that causes any of its targets to be charmed on a failed saving throw, thereby imposing disadvantage on the save. This effect applies only if the spell has a somatic or a material component.

The means that a spell qualifies if all of the following conditions are met:

1. The spell causes the Charmed condition

2. The spell calls for a saving throw which, if failed, inflicts the charm effect

3. The spell has a material and/or somatic component

The spells meeting these 3 conditions currently are:

• Animal friendship

• Charm monster

• Charm person

• Crown of madness

• Dominate beast

• Dominate monster

• Dominate person

• Hypnotic pattern

• Modify memory

Answer 2

As of the November 2018 DMG Errata:

Instrument of the Bards (p. 176). The final paragraph is replaced with the following: “You can play the instrument while casting a spell that causes any of its targets to be charmed on a failed saving throw, thereby imposing disadvantage on the save. This effect applies only if the spell has a somatic or a material component.”

There is no longer a requirement that the instrument be used as the focus, and it works as long as there is a somatic or material component. While the character still needs to be a bard to attune it, it can be used with non-bard spells.

Based on a quick filter on D&D Beyond, the list appears to be:

• Animal Friendship
• Charm Monster
• Charm Person
• Crown of Madness
• Dominate Beast
• Dominate Monster
• Dominate Person
• Hypnotic Pattern
• Modify Memory

Some of the spells under that same search (not listed above) are there because they cure or suppress the charmed condition. Of those that aren't curatives, a few others don't make muster for use with an Instrument for other reasons:

• Awaken imposes charmed, but has no save.
• Compulsion, Suggestion, and Mass Suggestion don't actually impose the charmed condition, despite un-charmable people being immune.
• Geas only has a verbal component.

Suggestion actually doesn't appear at all on that search, but Mass Suggestion does. That indicates there may be a problem in the site's indexing functions, so there may be other spells that reference the Charmed condition that aren't being found.

Answer 3

A casting of hypnotic pattern that imposes disadvantage on the save is entirely worth it. A half dozen opponents suddenly becomes effectively one or two, maybe zero. As powerful as that combo is, what more do you really need?