Is this homebrew "Thoughtseize" spell balanced? [Round 2]

Question

See the previous round of feedback on my original iteration of the spell here.

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I was inspired by the Thoughtseize card from Magic, the Gathering to create a spell that achieves a similar effect.

I intend to introduce this spell as something that must be studied extensively at an academy, is considered "new magic" but also probably taboo, and likely as something wielded freely by a villain or cabal. The PCs will be able to learn this spell eventually, but they can't just choose this spell when leveling their character unless they've done the necessary preparation. I haven't worked out what that is yet.

The spell is intended to be available to Bards, Wizards, and maybe Warlocks.

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The spell description:

Thoughtseize

2nd-level enchantment

Casting Time: 1 action

Range: 30 feet

Components: V, S, M (a needle or pin)

Duration: Concentration, up to 1 hour

You probe the mind of your target, and can sever a thread of their memory for a time.

Choose a creature you can see within range. The creature must succeed on a Wisdom saving throw. On a failed save, if the target can cast spells, the affected creature forgets one spell that is innate, prepared, or otherwise fixed in its mind that is one level lower than the spell slot used to cast this spell. You may choose which spell is forgotten from a list of valid choices. If no spells meet these requirements, you may choose a spell of a level lower than the level used to cast this spell, but of the highest level the target can cast. Otherwise, this spell fails.

When you cast this spell using a spell slot of 4th level or higher, you may cause the target to forget an additional spell for every two levels the expended slot was above 2nd. Additionally, for each spell you can choose beyond the first, you may select a spell up to a number of spell levels lower than the level used to cast this spell, equal to that spell slot level minus 1. You must announce the spell level(s) from which you wish to select before selecting any spell(s). You may only select a single spell from each spell level.

This effect lasts for the duration of the spell. While concentrating on this spell, you suffer 1d4 psychic damage at the beginning of each turn due to mental strain. This damage cannot be prevented by immunities or magical effects. If you use this spell to cause the target to forget more than one spell, you suffer an additional d4 of psychic damage for each spell chosen beyond the first.

I am looking for any and all feedback, but I am primarily concerned with whether this spell is balanced for PC use and/or for Villain use.

One phrase I'm particularly unsure about is from the first paragraph:

If no spells meet these requirements, you may choose a spell of a level lower than the level used to cast this spell, but of the highest level the target can cast. Otherwise, this spell fails.

Answer 1

This spell is sort of weirdly situational:

• You have to be fighting a single spellcaster, or a small number of spellcasters
• You have to know what level their damage spells are at (perhaps from seeing them use those spells against you)
• You have to have a spell slot available that's higher level than their damage spells
• You have to be far enough away from them that they can't just throw damage cantrips to break your concentration

Once you've gotten all that, this spell becomes a very strong save-or-lose spell. It's much better than (eg) hold person, because hold person grants a save every turn to escape it, and this spell doesn't.

This spell is unlikely to be useful in most adventures: if the group encountered a single spellcaster of the sort that they'd want to lock down with this spell, the spellcaster would probably have high-level spell slots the group couldn't lock down. If you're planning for your adventure to contain some scenarios where this spell would be useful, it seems fine to give the player characters the opportunity to learn it and use it. (And I imagine it would be very satisfying for them: "look who's locked down now!")

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You've asked if this is appropriate for villain use. I don't think it's great. Your spellcasters will feel like you're trying to nerf them by using a DM-created effect that shuts them down while leaving the fighters alone. I try to always have the villain do something that's a threat to all the player characters, not just one unlucky player character.

Your villains will work better if they just use damage spells (especially multi-target damage spells), because those work in every situation and will make everyone feel their character is in danger.

If you want to have your villains use an ability-loss effect, I recommend (1) attaching it to a damage effect, like "if you fail your save against this attack, you also lose one of your abilities", and (2) thinking of a fair way to let it have an effect on martial characters as well as spellcasters.

Answer 2

This spell is underpowered for a 2nd level spell

The description of the spell offers primarily combat benefits. In this case, Hold Person (2nd level) is superior option in combat situations. Paralysis will prevent the creature from casting all of their spells in addition to several other benefits.

The primary drawbacks of the Hold Person spell is that it can only target Humanoids, but most low CR spellcasters encountered are humanoid. Almost every combat ends before 1 minute has passed, making the duration difference negligible.

Suggested Modifications

Enhance the unique uses of this spell out of or before combat, as this is the niche the spell would fill.

1. Consider increasing the range of the spell to match or exceed Hold Person (60 ft) to allow stealth usage.
2. Consider removing the Concentration Requirement, allowing for more versatile usage, particularly before combat.
3. Consider giving the spell utility as a lower level or different version of the Modify Memory spell.