Forcing a saving throw to be made with disadvantage

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 spellcaster (dont know which class yet) who specializes in CC and spells like Phantasmal Killer, but I don’t feel like a high spellcast mod. would really cut the deal to make the CC a little more reliable.