Much less wasteful than having to burn another action and another high-end spell slot, plus fix whatever damage that opponent inflicts on your party before your initiative comes up again.
Take the Banishment example: You have already cast the spell (worth 7 SP) metamagicked with heightened spell (3 SP).
Casting Silvery Barb (2 SP) is much better value than casting Banishment (7 SP) again, for the same chance of banishing your opponent.
In terms of a spell slot, sure. But more than likely if he succeeded once he will succeed again and aside from the price in spell slot, there is also a price in spells known/prepared and in using your reaction.
I have never played a full caster that had all the spells I needed, even when I played high level wizards with spells via feats and races.
2) How many are capable of applying disadvantage to saving throws and attack rolls and ability checks cheaply?
But SB can't do this on a single use either. It can only affect 1 roll and only 1 time with a casting. So a better wording is capable of forcing a reroll to A saving throw OR AN ability check OR AN attack roll. Yes, the spell can be used for all 3, but only one at a time and only a single roll.
For comparison a 1st-level undead warlock can cause disadvantage on ALL attacks and ability checks for an entire turn and can do this every single turn at level 1 as long as he lands an attack (spell or weapon). This costs 1 bonus action and it is a free rider thereafter requiring no spell slot and in addition to disadvantage it also imposes movement restrictions. He can do this on every turn for 2 fights a day at first level and going up from there with PB. So at 1st level he will be able to affect more rolls a day than even a 20th level sorcerer will be able to do with SB without using higher level slots.
At level 3 any Warlock subclass can cause disadvantage to all attacks and abilities with a bonus action, again with no spell slot at level 3. This is at will, can be done every single turn all day long for the cost of a bonus action. It also lasts an entire minute, so after 4 turns he could have 4 different enemies getting disadvantage on ALL attacks and ALL ability checks for the next 6+ turns, where a caster of any level who used all of his 1st level slots on SB in the same battle will have affected a total of 4 rolls and will be done. To add insult to injury the Warlock has a flat 25% chance of making the opponent unconscious and incapacitated. The Warlock can keep going all day long.
An Undead Warlock level 3+ can stack both of these, giving 2 different foes disadvantage on all attacks and abilities every turn.
Bane can cause -1d4 to attacks and saves and do this for a full minute to 3 different foes and there are I think 16 different subclasses that can cast this at 1st level and I believe at least another 3 that can do this by level 3. All these abilities affect all attacks and ability checks or attacks and saves for an entire turn or an entire minute respectively.
So to answer, I would say on the order of 17 different subclasses can do something equivalent or better at 1st level. Another 8 subclasses by level 3.
Those are rough numbers but I think that is the ballpark.
3) How many can get access to Silvery Barbs?
I believe 9 of the above named subclasses can get silvery barbs. This assumes we are not including subclasses that can get it through attendance at the Strixhaven school. If we are counting that, then every subclass can get it.
And I am pointing out that this is a fallacy, because generally, you do not cast a spell that requires an opponent to fail a saving throw against an opponent with a good chance of making that saving throw.
Generally you do not know what they need to save and it is not uncommon at the tables I have played at to cast spells against enemies that are immune to them completely.
I tried to banish Bel a few weeks ago.
If their chance to pass is high, why did you cast the initial spell in the first place, rather than a spell that was more likely to have an effect?
Because you generally do not know this. Yes you can make some assumptions, but it is rare you know an opponents stats unless you have a character (Ranger, Fighter) that has this ability.
You have still spent the spell slot to cause disadvantage with this comparison spell before throwing your big spell. This means that it is exactly as effective at causing a failed save and more mathematically powerful, because using SB is "free" a significant amount of the time (when your opponent fails their save the first time).
As I said earlier, it is a more efficient use of spell slots than imposing disadvantage, but it will not cause as many fails.
It also is going to be "free" in terms of slots most often when the DC is high. When the DC is low it is not going to be "free" in terms of slots as often and not going to be effective as often. In both cases though you need to spend a known/prepared spell on it.
Let me ask you this - If you could use a bonus action to make someone roll 20 times and take the lowest roll or you have someone who rolled 19 times and suceeded every time and you are going to use a reaction make him roll one more time. Do you think these are equal? Do you think it is better to spend something on the second than on the first?
Wot?
The statistics would be the same, the only difference is that using SB you would save on spell slots. Generally more than 50% of the time.
No they are not. Causing disadvantage will always result in a greater chance of failure than making an enemy reroll a success.
Rolling twice with a random result is NOT the same as rolling a second time when a save has already suceeded.
Note that we are getting bogged down on spell save discussions quite a bit, which is only one facet of the capabilities of SB. If you don't get to use SB to punch spells past saves, you can use it for ability checks or attack rolls instead. Versatility is power.
I agree with this 100%
SB is a good spell and using it to cancel a ctitical hit is awesome. We are bogged down in the discussion on saves because people think that use is both primal and they think it is better than it is.
It is going to be rare that it will make an enemy fail a save on a game-changing spell. It will not be rare that it is useful.