My group is facing a very powerful boss, and is looking for various ways to lower enemy saving throws.
Currently we know of the following methods:
1) Heightened Spell metamagic
2) Bane
3) Bestow Curse
Are there any other class ability, spells, magic items, etc that can lower a person's saving throw?
Shadow Hound (Shadow Sorcerer) is a bonus action + 3 sorcery points summons that (in addition to the monster summoned) imposes disadvantage to ALL your targets saves while it's adjacent to your target.
Instrument of the Bards imposes disadvantage to saves vs Charmed condition from spells cast through it. Combine with
Hypnotic pattern for encounter auto-wins against anything that isnt immune to the Charmed condition.
Incapacitated, Paralysed, Petrified and Stunned creatures auto fail Str and Dex saves (and checks). Great on Battlemaster Monks (auto disarm, shove or trip your stunned target). Also spells like
Telekinesis and
Bigbys hand can do some good things to a stunned or incapacitated target.
Restrained is disadvantage on Dex saves.
Sickening Radiance inflicts exhaustion. Gain enough levels and you're at disadvantage to saves.
The
Curse spell.
The
Contagion spell (save varies depending on the sickness given).
Something from left field... the Persuasion skill can impose disadvantage on Saves. Use it to convince your target to seek out a Mummy Lords treasure and take some. If you roll well enough and they agree to do this, they're cursed (disadvantage on Saves).