Originally Posted by
Gtdead
Powerword: Kill
This one suffers from another problem, namely the 1 spellslot per day. You want your 9th spellslot to be more versatile than that. However if you know that you have to do a boss fight, and you are already prepared with your simulacrums, contigencies etc, PW:K is a good idea because you can calculate the average damage of the party and bring down the big bad in 1 or 2 turns. Dealing with minions then is easier.
For example against a tarrasque (676) as a lvl 20 party with +3 items etc (I'm not an expert on magical items so this will probably not be optimized):
(I've used a damage calculator I've built for most of these values)
The hasted (wizard concentration) samurai can do 130~ dpr with action surge (546) - +3 Bow
A multiclassed (sorc or fighter dip) tempest cleric with call lightning can do 180 damage or 90 if legendary resistances are used. (366 or 456) - Tome of Understanding
An EA hasted (simulacrum concentration) tenser transformed valor bard (Bard concentration) with foresight + swift quiver can deal 75~ (291 or 381) - +3 Bow
The simulacrum can try an upcasted disintegration for 96 or 0 (LR) (195 or 381 (no more LR))
A hasted (paladin concentration) vengeance paladin with 2 5d8 smites can deal 110~ (85 or 271) - Fire Giant's Belt, +3 GS
So there is a scenario where a power word kill can seal the deal.
Of course this can all go sideways if the damage rolls don't work that well or the tarrasque rolls 20 on dex saving throws or party can't prebuff or the party gets counterspelled or or or, but it's a possibility and perhaps it's worthwhile to prepare it.