I'm back with another homebrewed thing. But, I can't decide on a reasonable cost for it. See below:
You spend X Sorcery Points. You modify a spell with a range that is not Self or Touch, has a casting time of 1 action, and a duration of Instantaneous.
The spell you cast changes in the following ways:
- If the spell forces a save DC, roll a spell attack instead. You deal 0 damage on a miss. If you hit, multiply the damage dealt by 1.25
- If the spell is not single target, it becomes a single target spell. If the spell has area effects, it only affects the single target of the spell. If it also deals damage, multiply the damage by 1.5
The idea is to maximize the damage dealt by turning your normal spell into an attack spell against a single target -- basically trying to turn every spell into Disintegrate.
Justification of 50% Damage Boost
So that people don't pass too quick a judgement off this as possibly "too powerful" or "too weak," I'd like to break down the numbers here.
I based the 50% damage increase off of the One Target vs Multiple Targets table in the DMG.
DMG pg. 284
Spell Level One Target Multiple Targets Cantrip 1d10 1d6 1st 2d10 2d6 2nd 3d10 4d6 3rd 5d10 6d6 4th 6d10 7d6 5th 8d10 8d6 6th 10d10 11d6 7th 11d10 12d6 8th 12d10 13d6 9th 15d10 14d6
The DMG says you can create a new spell with damage appropriate for its level by keeping the mean value of its damage around the same as the mean values of the dice shown in the Spell Damage table.
DMG pg. 283
You can use different damage dice than the ones in the table, provided that the average result is about the same. Doing so can add a little variety to the spell. For example, you could change a cantrip's damage from 1d10 (average 5.5) to 2d4 (average 5), reducing the maximum damage and making an average result more likely.
On average, the mean values for single target spells according to that table is 50% higher than multiple target spells, so to compensate for the fact that this spell forces a multi-target spell to become a single-target one, the damage is scaled up by that amount.
Justification of 25% Damage Boost
If saving from a spell successfully causes you to take half damage, then its maximum possible damage is 25% weaker. The Spell Damage table assumes you take half damage on a successful save, but advises increasing the damage by 25% if targets take no damage from a save.
DMG pg. 283
For any spell that deals damage, use the Spell Damage table to determine approximately how much damage is appropriate given the spell's level. The table assumes the spell deals half damage on a successful saving throw or a missed attack. If your spell doesn't deal damage on a successful save, you can increase the damage by 25 percent.
Since this spell forces you so that your targets take no damage if your attack roll misses, I compensate by boosting damage up 25%
Closing Remarks and Dilemma
This metamagic changes the way the spell is cast while trying to abide by fair tradeoff rules according to the DMG. This probably gives it a minimum cost of at least 1 SP (and not a higher minimum) because the trade off is fair.
However, it does have a significant benefit. It replaces save DCs with spell attack rolls. This lets you use things like Advantage and Inspiration on your roll to boost your attack. It is not necessarily a strong effect, but with the right party/preparation, I think it can be.
My dilemma is, I can't decide the appropriate total SP cost. I can't seem to find a spell that provides similar advantages to form a basis.
Remembering that 1 spell slot = 1 SP, how many SP should this metamagic cost?