I've been trying to create a monk subclass that excels at fighting spellcasters. Think Ty-Lee from ATLA, except it hinders mages instead of benders. I'm having issues keeping it balanced, so I thought you guys could help. (side note: feel free to make and/or use and/or publish your own versions because I'm not planning on making money off of it.)

The main feature is a 3rd level ability called Hindering Strike. When you hit a creature with an unarmed strike you can spend 3 ki points to force it to make a CON save. If it fails it must make an additional CON save each time it tries to cast a spell for 1 minute. If the target of Hindering Strike fails one of these saves, the spell doesn't take effect but they don't lose that spell slot.

How can the higher-level abilities build off of this feature and does it need adjusting?

The target will automatically have to make a concentration check when they get hit anyway. It might be more in balance to have it only cost 1 Ki and have it impose Disadvantage on that check and not have the additional (very OP) minute long rider. Or maybe have it impose Disadvantage on Concentration checks until the beginning of the Monk’s next turn for 2 Ki.

Quote from IamSposta >>

The target will automatically have to make a concentration check when they get hit anyway. It might be more in balance to have it only cost 1 Ki and have it impose Disadvantage on that check and not have the additional (very OP) minute long rider. Or maybe have it impose Disadvantage on Concentration checks until the beginning of the Monk’s next turn for 2 Ki.

A target will only normally make a CON check if it's actively using a concentration spell, some spellcasting monsters don't have many (or any) of those, so it does definitely need some way to interfere with instant/non-concentration spells as well to be useful.

I quite like the idea, but I wonder at the cost; 3 ki points is all you'll have at 3rd level I think, so it might make sense to make this easier and less powerful but cumulative. Something like:

When you hit with an unarmed strike, you can spend 1 ki point to interfere with a target's spellcasting ability. Until the end of their next turn, whenever they attempt to cast a spell they must pass a Constitution saving throw against your DC or the spell will fail. If the target is already subjected to this effect, the duration is instead extended by one round.

My wording might be a little clunky, but hopefully you get the idea.

Just throwing ideas out there, to me this ability seems pretty expensive at low levels, but can become pretty broken at high levels. Also, mages tend to stay in the back, away from melee. My idea would be that when a creature tries to cast a spell within 60 feet of you, you can use your reaction to cast counterspell, expending a number of ki points equal to the level you want to cast it at. If you cast it this way at a lower level than the spell you're trying to counter, and succeed, then you regain ki points equal to the spell's level. Maybe at higher levels, when you use this feature, you can expend another ki point to make an unarmed strike against the caster (you don't have to be within 5 feet to make this attack, like how thorn whip is a melee attack but has a range of 30 feet). I haven't personally played monk though, so this is just my idea.

Ty Lee's abilities in ATLA is basically a Stunning Strike which is a class ability anyway.  I would recommend the following to add on to that:

1) level 3:  creatures have disadvantage on saving throws to maintain concentration when hit by your unarmed strike/monk weapon + deflect missiles can work on ranged spell attacks (without redirecting them)

2) level 6:  Ki points to cast Counterspell /Dispel Magic (3 or 4 Ki points, lines up with the costs for Shadow Monk spells (ki = spell level) and 4 elements (ki = spell level + 1))

3) Level 11: Advantage on saving throws against spells

4) Level 17:  Resistance to Spell Damage and Damage from Magic Weapons (duration 1 minute, either Ki cost or 1/short or long rest)

Thoughts?

Quote from iconarising >>

Ty Lee's abilities in ATLA is basically a Stunning Strike which is a class ability anyway.  I would recommend the following to add on to that:

1) level 3:  creatures have disadvantage on saving throws to maintain concentration when hit by your unarmed strike/monk weapon + deflect missiles can work on ranged spell attacks (without redirecting them)

2) level 6:  Ki points to cast Counterspell /Dispel Magic (3 or 4 Ki points, lines up with the costs for Shadow Monk spells (ki = spell level) and 4 elements (ki = spell level + 1))

3) Level 11: Advantage on saving throws against spells

4) Level 17:  Resistance to Spell Damage and Damage from Magic Weapons (duration 1 minute, either Ki cost or 1/short or long rest)

 

Thoughts?

 
This is a well-trodden path in homebrewing--the anti-caster. I have a similar archetype I can share, but the fundamental issue is that creating an archetype with a singular focus is a huge disadvantage in most games. Most monsters don't cast spells. Many more that use magic don't directly do so through spells (think barbed devil and hurl flame). As a result, in most scenarios, your archetype gives you no additional tools.

My recommendation is to broaden the abilities. Here's what I'm toying with for my monk:

-Extends deflect missiles to work with all ranged attacks, including ranged spell attacks, and magic missiles. Also allow them to deflect missiles from adjacent creatures.
-When an unarmed attack causes concentration to break, deal damage proportional to the spell's level. Also allow stunning strike to end spell effects like dispel magic on hostile enemies, up to a relatively low spell level cap.
-When a creature casts a spell, use reaction to teleport with advantage on next attack (similar to shadow monk). Also, cast misty step using ki.

Note that I try to give each ability a use for non-caster encounters. I'm not quite satisfied because it's too combat-heavy, but you get the drift.