THE BFSD (5e Optimized Character Build)
From D&D Wiki
BIG F***ing SPELL DAMAGE.
The initial main purpose of this build was to kill a Tarrasque, one of the strongest creatures in D&d, but as I continued to optimise the build I found that it could do so much more...Here is how to kill gods and break the weave of magic. The build requires you to be a minimum of a 14th level spellcaster.
No particular race is necessary, but in my opinion the best races for this build would be: Human Variant: For that free feat.
Elf (Any subrace): For that 1000 year life span, to outlive the Mine Turtle Combo.
There are no other races that can assist in this build. The best possible feat for the build would be Elemental Adept (Thunder), to effectively double the absolute minimum damage output. Or the Resilient feat to get proficiency in Dexterity Saves.
Background & Skills
Up to you.
Your highest score should be CHR, followed up by DEX. The rest of the ability scores are up to you.
12th level sorcerer, any archetype will do, although wild magic is preferred. 2nd level wizard. Must be of the Lore Mastery school. If you have an extra level in your game, you can put it in either of the classes and use the *Turtle mine combo*.
You need to learn one 7th level spell, Delayed Blast Fireball. If you are going for the *Turtle mine combo*, you need the 8th level spell, Sequester and of your choice between the 1st level spell Find Familiar or 2nd level spell Flock of Familiars. You need the Extended Spell metamagic option. Maybe a timer? If Dm isn't cool, grab a scroll of polymorph or a buddy that can cast it.
Shield Master Feat: For taking this reality breaking exploit. Elemental Adept: For effectively doubling the lowest possible amount of damage. Lucky: To make sure they fail. I'm sure there are others, be sure to add on your own accord to make the exploit better.
Cast a 7th level Delayed Fireball, expend all 12 of your sorcery point to extend the duration to the maximum of 24 hours. This spell does at a base: 12d6 Fire damage and adds a d6 every round of combat (effectively every 6 seconds in-game time), so here is some maths. 12d6 (Base) + (10 x 6 ('D6 per minute') x 60 (D6 per hour) x 24 (D6 per 24 hours)) = 86,412d6 of damage at a minimum = 172,824 of damage at a minimum if you have Elemental Adept.
But this alone would not kill a Tarrasque, after all it has fire immunity, how can we get past that? Simple, those two levels in wizard.
Spell Secrets At 2nd level, you master the first in a series of arcane secrets uncovered by your extensive studies.
When you cast a spell with a spell slot and the spell deals acid, cold, fire, force, lightning, necrotic, radiant, or thunder damage, you can substitute that damage type with one other type from that list (you can change only one damage type per casting of a spell). You replace one energy type for another by altering the spell’s formula as you cast it.
When you cast a spell with a spell slot and the spell requires a saving throw, you can change the saving throw from one ability score to another of your choice. Once you change a saving throw in this way, you can’t do so again until you finish a short or long rest.
By changing the damage type and even the save you can even bypass evasion and damage immunities. All you have to do is cast the spell, wait 24 hours let them trigger it or throw the bead (Resilient feat can assist in this) at them.
MINE TURTLE COMBO
This combo varies based on DM leniency. First, do the Delayed Blast Fireball exploit, have your familiar pick up the bead right before its timer goes off, then Sequester the familiar and name a condition at which it deactivates. This extends the Delayed Blast Fireball timer indefinitely so long as the sequester is active. If your DM wishes to dispute that Sequester doesn't do its freezing effect on objects carried by living creatures, so use a scroll or have a buddy cast polymorph on the familiar carrying the bead, this way the bead and familiar are one creature. So make a frozen turtle and leave it be for some poor peasant to set off and be sent to the shadow realm.