When you absolutely, positively, need your save or suck target to fail.

So I’ve been looking at building characters and getting down the perfect debuffer… and I think I nailed it… it doesn’t come on fully until player level 12 but once you hit 12 nobody will ever be able to make the save dc on your save or suck spells again. It’s level 6 eloquence bard due to unsettling words. It’s a bonus action that the target rolls a d6 and subtracts it from the next save they roll. And the other half is shadow sorcerer 6. They get Hound of Ill Omen which is a bonus action and if the target is within 5 feet of the hound they have disadvantage on all saving throws for spells you cast. I understand that this is two bonus actions but you can use the hound and then vicious mockery, or bless, or bane (if your save or suck isn’t concentration). Then on your next turn use the bonus action to use unsettling words and then hit them with your save or suck. So if you ever need a spell to stick, this character can do it.