My experience is from actual play. It is what pointed out to me how OP the spell can be. It gets worse and worse the higher level you go. At low levels it is just a different/worse shield. When used against attacks it is fine. When used against skill rolls, it is interesting. When used to push through spells it is OP.
Ok so here is the math on this and why you are wrong mechanically -The problem is that enemies generally have a very small chance of resisting spells at high level, unless you are using something that is clearly the wrong spell. It takes a 1/5 chance of resisting and makes it a 1/25 chance.
At high levels most relevant enemies have legendary resistance, which makes it useless for this until you run them out.At high levels it is the opposite of what you are describing. It makes landing a spell on an enemy way too likely. There is no real price for failing your 5th level slot, you just spent a 1st level spell and effectively get another try at a high level spell.
When it was letting you reroll a save on a hold person etc it was powerful but not insane. When a 1st level spell is basically giving you another chance at Dominate Monster, or Banishment, it is OP.
I concur. It's not so much that it's too powerful, it's that it's a pain in the butt. It's bad design (and I'm not insulting the designers here - it looks good on paper - it's just that it's not good for the game.)I can't vote here because I don't necessarily think I can comment on balance, but I do have some thoughts on the spell.
I was originally fine with it. Did it seem strong? Maybe, but I didn't freak out about the strength of it.
Seeing it in play, I find it atrocious. Even if it isn't OP, every time a player shouts out "SILVERY BARBS!" the game grinds to a halt with forced rerolls, determining who to give the Advantage to, having to remind people to use the Advantage. It's also, so far, felt very divorced from the fiction and feels more game-y than I thought it would.
In what way? If cast when an enemy has a 80% chance of failing a save, but made the save in question, it has a 80% chance of success. You only choose to use it once you're already in the situation where they made the save. What specific misunderstanding do you feel people have regarding the math, or what math are you thinking of which makes it less effective, in the situations in which it would be used?I guess the problem with this spell is there are an awful lot of people who don't understand the maths, and therefore think it is a lot better than it really is.
Which means probability that Silvery Barbs actually made any difference to the outcome = 16%.In what way? If cast when an enemy has a 80% chance of failing a save, but made the save in question, it has a 80% chance of success. You only choose to use it once you're already in the situation where they made the save. What specific misunderstanding do you feel people have regarding the math, or what math are you thinking of which makes it less effective, in the situations in which it would be used?
Reducing the chance of a negative outcome from 20% to 4% may only be a "16% chance it actually made a difference", but it's also an 80% reduction in the rate of undesirable outcomes, and of the total 84% of situations in which it "didn't make a difference", you were not using it, and expended no resources, in 80% of those.Which means probability that Silvery Barbs actually made any difference to the outcome = 16%.
And YOU DIDN'T NEED IT. You could have prepared a different spell instead, perhaps one which your foe would have had a 0% chance of saving against. As a highly situational cure for really bad luck, the spell isn't bad, which is why it is rated "good" rather than "suck". But it's a long way short of overpowered. And the alternative scenario, when your foe has a high chance of successful saves, is most likely to result in burning a 1st level slot and your reaction for no benefit at all.Reducing the chance of a negative outcome from 20% to 4% may only be a "16% chance it actually made a difference", but it's also an 80% reduction in the rate of undesirable outcomes, and of the total 84% of situations in which it "didn't make a difference", you were not using it, and expended no resources, in 80% of those.
Right, but as outlined in the very next paragraph, a small chance of it coming up in an individual circumstance rapidly becomes a large chance of it coming up during a large encounter. The more difficult the encounter, the longer it is likely to take, and the more saves you'll likely be forcing upon the enemy, and therefore the more likely it is to come up. A 54% chance of coming up and impacting an encounter is not "highly situational". Obviously the fictionalized 'everything has a 80% chance' scenario isn't real math, but it's a close enough approximation to demonstrate the point, which was ignored. A 20% chance of a situation coming up Per Incident rapidly rises to a high probability that it will come up.And YOU DIDN'T NEED IT. You could have prepared a different spell instead, perhaps one which your foe would have had a 0% chance of saving against. As a highly situational cure for really bad luck, the spell isn't bad, which is why it is rated "good" rather than "suck". But it's a long way short of overpowered. And the alternative scenario, when your foe has a high chance of successful saves, is most likely to result in burning a 1st level slot and your reaction for no benefit at all.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.