Turn 1: Mark of Death
Turn 2: Striking Spell (2 actions) + Bespell (free) + Poison Weapon (1 action) all work until the end of your next turn.
Turn 3: True Strike + Assassinate.
Decent chance you will crit, which will also improve the spell.
True Strike needs verbal, which will cause the assassinate's "target must be unaware" constraint to fail unless target is deaf. You would need Silent Spell feat which is an action.
Yea, bespell is also until the end of the current turn, I miss read that. But this works with Power Strike.
Turn 1: Striking Spell (2 actions) + School Shroud (?) + Poison Weapon (1 action)
Turn 2: Turn 3: True Strike + Bespell + Power Strike
Maybe..
Turn 2: Eldritch Shot (Eldrich Archer) = 2 spells + 1 arrow + 1d6.
Not overpowered or anything since it took a whole turn to setup, but still seems like it wins for biggest single attack.
I prefer this gem I came up with while sleep deprived. Shamelessly copy/pasta'd from a previous post:
Actually, if you really like putting all your eggs in one big ol'basket, you could store a Striking Spell, then use Eldritch Shot, which includes a Strike on the subsequent turn to have 2 spells go off in one big attack, with one of them having it's effect determined by the attack roll.
If that's not enough of your spellcasting resources, use a level appropriate Spellstrike Arrow for these shenanigans. Then you could in theory Poison the ammo.
If that's still not enough, get yourself an Alchemical Crossbow and slot in an appropriate bomb for that extra d6.
For 3 turns and 3 of your 4 Spells, this gives you a SERIOUS punch... that can completely miss with one roll.
Sorry, I was thinking this up as I was writing it. Seriously not worth it, but someday I'm going to make this character. And the one session I play him in will be glorious.
Edit: I will name him: Gene Starwind.
If that's not enough of your spellcasting resources, use a level appropriate Spellstrike Arrow for these shenanigans. Then you could in theory Poison the ammo.
If that's still not enough, get yourself an Alchemical Crossbow and slot in an appropriate bomb for that extra d6.
Don't forget a talisman.