It still fits your criteria, which was a single target save based damage spell. It may not be area, but honestly, didn't you want single target? It just doesn't get extra damage out of it because, well, its Force, which mean besides working on things others wouldn't, virtually nothing has resistance to it.
I want single-target save spells that do significantly more damage than same-level AOE spells, or possibly a little more damage but have some neat debuff at the same time. If I'm using my limited high-level spells, I want the monsters to
feel it.
I've had great success with Flaming Sphere, Magic Missile, Sudden Bolt, Lightning Bolt, Fireball, Disintegrate (+True Strike), against single targets.
I tried using
flaming sphere at the early levels, but quickly realized it was a waste of a spell. It would have been cool if the designer hadn't decided that repeatable 3d6 damage was too much, and put in the clause that it deals no damage on a successful save. If it hadn't had that bit, it would have been quite a neat little tool in the box, but as is it's useless.
Take
Lightning Bolt for instance on a base level 5 Wizard that just got it, cast against a
Level 8 Chimera-- the base level 5 wizard has a spell dc of 21 and the Chimera has a +16 Reflex, meaning it succeeds on a 5. But, if it rolls anything below a 15, takes half damage-- reflex is its middle save. So it actually takes damage from the lightning bolt most of the time, increasing with frightened, which is a thing parties usually want to inflict.
Lightning Bolt does 4d12 damage, which averages to 24 damage, doubles to 48 damage if it crit fails (requires a 1 here), and 12 average damage if the target succeeds its saving throw, the chimera has 135 HP. If you get your 1/4th failure chance, and my 2 am math isn't mistaken you've done 17% of its health, if you get your 2/4 succeeded save you deal about 8.5% of it's health, with nothing happening on the remaining fourth. That's without the 1/20 odds of it rolling the 1 on its save and you dealing 34% of its health with one spell, or you rolling better on damage, or any modification from the frightened conditions (or any other conditions) that the whole party loves, and you have a leftover action-- my wizard used its evocation school force bolt to add extra damage.
Your math is slightly off, but not by much. The chimera has a 30% chance of a critical success, 50% chance of a success, 15% chance of failure, and 5% chance of a critical failure. That averages out to 50% damage, or an average of 13. That's less than 10% of its hit points, and that's me throwing my biggest spell at it. A spell that has an almost one in three chance of doing
nothing. And that's against a monster where Reflex is the middle save.
Given your odds of dealing something every round and the fact that this is a solo boss, that's not bad if AOE is what you have prepped. Sudden bolt does even better (being a lower level single target version of lightning bolt with 1 per level scaling), since it's actually 5d12 at this level, averaging to 30 full damage and 15 half.
Your example is a wizard, so what is the chance that they have multiple
lightning bolts prepared? You have 2-3 spell slots, depending on whether you're a specialist or a universalist, plus Drain Bonded Item. I'd argue that having more than two
bolts prepared, plus the Bonded Item, is very unlikely, and if this is a "boss" fight you might very well have spent some before. Paizo
loves putting PCs through big 10+ encounter dungeons, wearing casters down before the end.
And again,
sudden bolt is an uncommon spell that comes from a particular adventure. The chances of any PC having that spell is miniscule, particularly if you're not playing the Extinction Curse. Given that both the Advanced Player's Guide and Secrets of Magic have been released after that adventure, and without any similarly-scaling single-target spells in them, I think it's safe to say that Paizo considers the spell an accident of early development, and really a little more powerful than spells should be.
If we go the up cast Magic Missile route here (which I loved on my Wizard), your level 3 slots using all 3 actions are providing 6 darts, worth a total of 6d4+6 damage, which averages to 18 damage which is 13% of the Chimera's health every turn you do it, going up or down by chance. Considering your martial's numbers are balancing their hits and crits with complete whiffs, that's really not bad at all for a single turn for 1/4th to 1/6th of the party. If a combat lasts four rounds, and you keep it up, you'll have done 52% of the bosses HP personally.
Assuming you have three
magic missiles prepared (which means you're an evoker) and unused, that you haven't used your Drain Bonded Item ability before the fight, and that you never need to move in the fight.
But
magic missile is actually a fairly good anti-boss spell, because it ignores their superior defenses. Too bad my character can't have it.
Thing is, overall a level +2 (maybe not +3) fight is "balanced". Taken as a whole, putting in the numbers at one end and getting a result a few rounds later in the other, it works out. The problem is the
way it is balanced, by giving the opposition a pretty big chance of ignoring your actions entirely. And that doesn't feel great.