Path of the Berserker- 6th level can't be charmed or frightened
Bardic Inspiration Dice
Bard's Counter Charm
Nature's Ward- Circle Druid, Can't be charmed or frightend by elementals or fey
Indomitable- 9th fighter, saving throw reroll
Stillness of Mind- MOnk 7-ends the effect of frightened or charmed
Purity of Body- MOnk 10- immune to poison and disease
Diamond Soul- MOnk 14- proficiency on all saving throws- can also reroll if use ki point
Divine HEalth- Paladin 3- Immune to disease
Aura of Protection-- Paladin 6- bonus to allies saving throw
Aura of Courage- Paladin 10- you and close allies can't be frightened
Cleansing TOuch- Paladin 14- end the effects of one spell on you or another
Aura of Devotion- Paladin 7- you and close allies can't be charmed
HOly nimbus- Paladin 20- advantage on saving throws on spells cast by undead
Slippery Mind- Rogue 15- gain proficiency in wisdom saving throw
Bend Luck- Sorcerer 6 (wild mage)- 1d4 to saving for an ally
Beguiling DEfense- Warlock 10 (Arch fey)- immune to charm
Dark One's own luck- Warlock 6 (fiend)- +d10 to one save
Dwarves have advantage against saves against poison
Elves and half elveshave advantage against being charmed and can't be put to sleep
Halfling's have lucky (reroll 1's) and have advantage against being frightened.
Gnomes have advantage on saving throws vs magic (INT, WIS and CHR only)
That's 22. Do you want me to go through the spells?
Thank you for doing this. I was aware of many of these.
But, I have to say, the list has so many holes (lots of other effects missing, or issues if a given class is missing, or the PC has to be capable in order to use the ability) that one could drive a truck through it.
For example, no Paladin or Monk, list down to 13. Also, few of these are like the Paladin auras where they can affect other PCs quickly or easily. By this, I mean that ability to buff others AFTER an effect has occurred is the same problem as the party healers healing a PC after the PC has fallen. Let's take a group of 2 PCs. One PC is incapacitated. Next round, the other PC gives that PC a bonus save. Well, the save is +1 vs. DC 18. The bonus save is all nice and well, but chances are, he'll miss the bonus save too. So, PC 1 gave up his action in order for PC 2 to miss yet another save. It becomes a death spiral.
By the way, advantage increases average dice roll by a little over 5 in mid-range scenarios (i.e. middle 50% of dice being needed). It only increases average dice roll by a little over 3 in extreme range scenarios (i.e. you need to roll 18 or higher on the die). Advantage is awesome in the middle range, not as awesome at the extremes. Just saying.
I definitely get what you are saying. And I know that spells can and will make a difference. But in order to get to level 15 where the Rogue gets the Wisdom proficiency, the party has to survive levels 1 to 14.
You have also illustrated that having a Paladin in the group is very helpful in regard to this.
But, my point is not that there are not ways to work around the issue. My point is that if those workarounds do not exist or are not available (e.g. casters are taken out), then TPKs might be a lot more frequent than people might expect. I hope I'm wrong. I suspect I'm not.
Giving someone advantage on a save when they have +1 vs. DC 18 ups their chance from 20% to 36% (hence my advantage ~=+3 comment above). Ok, but not exactly stellar. I suspect that some of the class / race capabilities that you have posted above will be a lot less effective in theory than in practice, especially at real high levels. At mid-levels with DC 13, yeah, those abilities will help a lot.
Time will tell.
PS. I am really concerned about this when one adds surprise into the mix. Having the monsters lay down an entire round of effects can take out more than 60% of a team. It might incapacitate most or all of the team for one or more rounds.