Forcing a saving throw to be made with disadvantage [closed]

Question

I know there is already a similar question, but it doesn't really give me an answer. Is there such a thing as a feat or an item that causes enemies to make saving throws like wisdom or general saving throws with disadvantage?

I wanted to create a mage (don't know which class yet) who specializes in CC and spells like Phantasmal Killer, but I don't feel like a high spellcasting mod would really be sufficient to make the CC more reliable.

edit: Based on comments and uncertainties, I would like to say that all ways to increase the likelihood that the spells will apply its effect are helpful. It doesn't have to be a disadvantage. It can also be an effect that increases my spell mod or decreases enemy saveroll as long as it can be used with a mageclass.

Answer 1

The Sorcerer Metamagic: Heightened Spell

When you Cast a Spell that forces a creature to make a saving throw to resist its Effects, you can spend 3 sorcery points to give one target of the spell disadvantage on its first saving throw made against the spell.

That would be the only such feature coming to my mind right now. Of course since it is a metamagic, it is difficult to use as an orientation for creating another class, but at least we can see that it costs a lot of sorcery points just to give a single target disadvantage on a single saving throw. That means the designers valued this effect extremely highly and you should be careful not to give it out too freely when building a class around it.

Answer 2

Magical Ambush - Rogue Arcane Trickster

This is a class feature that you gain at Level 9 that imposes disadvantage on spells you cast when hidden from your target.

Answer 3

Unearthed Arcana: the Mind Sliver cantrip

The Mind Sliver cantrip from the most recent Psionics Unearthed Arcana article is a damaging cantrip that gives the target a 1d4 penalty on the next save it makes before the end of your next turn if it fails its save against the cantrip.

This does involve another spell and require the target to fail a saving throw, but as it's a cantrip, you won't be using up your limited numbers of spell slots on it. It's not disadvantage, but as another mechanic that increases the likelihood of a failed save, it seems relevant enough to mention.

It's available to Sorcerers, Warlocks and Wizards; if you're not playing one of those, the usual cantrip access routes like being a High Elf or taking the Magic Initiate feat would also work.

As noted in the article, this is playtest content, so it's possible your DM won't allow it.