What are all the spells in any officially published sourcebook for 5e where a target is granted the option to deliberately fail their saving throw?
These are all the published spells (as of August 2019)
- Bones of the Earth (XGE, 150): A creature can choose to be lifted by a pillar of earth, instead of resisting it
- Calm Emotions (PHB, 221): A creature can choose to have their emotions calmed (Charm/Fear effect suppressed, hostility suppressed) instead of resisting it
- Scrying: (PHB, 273): A creature can choose to fail the saving throw if they want the caster to scry on them, and are aware the spell is being cast
- Watery Sphere (XGE, 170): A creature can choose to be restrained by the sphere
These spells allow a creature to be willingly affected without a saving throw (only unwilling targets must make the save)
The main difference is that with the prior list, the creature still makes the saving throw, but chooses to fail it. For this list, if the creature is willing, then they do not make a saving throw at all. This can be relevant for other effects which may or may not affect a creature's ability to pass or fail a saving throw.
- Enlarge/Reduce (PHB, 237): A creature can willingly be targeted by the spell to be enlarged or shrunk
- Levitate (PHB, 255): A creature can willingly be targeted by the spell to rise into the air
- Mass Polymorph (XGE, 160): A creature can be willingly transformed into a different creature
- Plane Shift (PHB, 266): The spell assumes target creatures are willing, but has stipulations for the situation where a creature is unwilling
- Polymorph (PHB, 266): A creature can be willingly transformed into a different creature
- Seeming: (PHB, 274): A creature can willingly have their clothes' appearance altered
- True Polymorph (PHB, 283): A creature can be willingly transformed into a different creature (or object)