Endgame, damaging spells weren't nearly as helpful as guardian angel and magic/missile protections.
Spells that target "all enemies" are great, but quicksand, asphyxiations, and death wish became my go-to spells for the most part in AP. The other spells could do 20-80 damage to all enemies depending on their resistances. If I landed a high hit, I'd keep using that spell and reserve the instant deaths for another fight.

Use EVERY cloud spell on mobs. They're fantastic! Granted, most of the time they nickel and dime, but it's free damage every round.

I had Powercast in the 70s-80s for my mage only. They're spells definitely hit *a lot* harder. I don't know if powercast only extends max power spells.

Keep in mind, from what I can tell, non-divinity casters lose well over half their efficacy without powercast.

First part:

Vi - self guardian angel in the first round; then mage, then Ranger
(can't remember if I forced Miles or not)
Lord - self guardian angel in the first round; then Samurai
Lord - self guardian angel in the first round; then Monk
Monk - had mind flay, but it nerfed after level 35ish
Samurai - had nukes, but they didn't do much.
Mage (only one with powercast damage spells remained relatively useful.
Ranger Summon elemental max level; ranged; summon again.

With an all magic party, I'd probably go with the below. Three elementals, and as many res powders as you can carry.
Front row would be priests - maybe cross class Psionic to Monk for 1 level to get stealth; a huge sidetrack depending on your race/stats

Priest - banish, death wish, falling stars - buffs and heals
Priest - banish, death wish, falling stars - buffs the other priest doesn't have
Mage - max out air soon for asphyxiation
Mage (or alch)
Alch - max out earth for quick sand
Psionic - fire and mind for prismic chaos and mind flay

I really like Toxic Cloud, as it doesn't just do damage; it can also inflict status ailments that can cause enemies to lose some of their turns.

There's also Death Cloud, which has a chance of outright killing anything affected every round; like other death spells, great to use against lower level enemies with high HP that don't have too much Air resistance.

(Note that instant death does not work at all against undead. I don't remember if Toxic Cloud is useful against undead, but I seem to remember androids being able to be knocked unconscious. For undead, Freeze Flesh/All is a status ailment that actually works (and that the dispel ability of the cleric and bishop will try to inflict).)

Edit: Also note that cloud spells, more so than other spells, benefit from higher power levels, as it affects both damage per round and duration (and hence the number of rounds the damage occurs). Ring of Fire works similarly to a cloud spell in this regard.

Edit 2: s/could/cloud

In the above party you'd get 2 turn undead opportunities, and 2 characters with banish that affects all undead within range. Oddly, while it only affects undead, it also looks like it does more damage than is listed. Possibly due to a realm weakness on the undeads' part.

I don't think I've ever tried any of the cloud spells on undead. I'll have to try it next time I fight undead.

I think draining cloud is my favorite for large groups. Nothing quite like going from a OH Sh!T to a chunk of the mob passing out due to no stamina.

Instead of 2 mages or 2 Alchs, 2 Psionics would be beneficial for an all magic party due to 2 castings of Might to Magic. Just make sure it's not cast the first couple rounds or you'll just ping pong SP between them.
BUT, that will remove the massive melee benefits from the added elemental.

I haven't noticed Draining Cloud significantly affecting Stamina or SP. (Then again, since enemies get infinite SP, that aspect of the spell only affects the party, but it still seems to be minor even on the party.)

Toxic Cloud is fun, as the enemies will be afflicted with status ailments every round, and even when the cloud runs out, the status ailments don't immediately disappear.

The most common situation for an enemy to run out of Stamina, in my experience, is when the enemies are using breath attacks, as they consume a significant amount (as anyone who's used Dracon breath will know).
The castch is that it can be a bit hard to predict who gets the SP.

My favorite Psionic spell is Psionic Blast, mainly because it's the only damage spell that isn't affected by line-of-sight. So, for example, in an area like the Rapax castle (or even the courtyard), you can attack enemies that can't even see you with that spell.

(For spells from other realms, I really like Quicksand from Alchemy (PL1 can still be useful against certain enemies, like low level enemies with high HP), and Restoration from Priest (it's basically the return of MADI from Wizardry 1-5; Wizardry 6-7 lacked this spell and sorely needed it; it's actually the only learnable spell that can cure Unconsciousness). I also love the Heal All spell. Of course, after typing this out, I find myself wishing that Restore Health were learnable, so that it would
be possible to use non-Divine SP for healing.)
Banish also works on demons and summons (though for summons I generally prefer to use Instant Death or Turncoat).

Also, Pray for a Miracle can mimic a variety of spells, and one of them is Turn Undead (which, by the way, is a 2nd level spell, in case you were wondering).

I don't know how you block it out like you did lol.

Is mindflay affected by LoS? It hits all enemies in range; Psionic blast hits just one group.
Any explosive can "go around walls" as long as more than half the targeting ball is visible; still needs to be within the blast radius though - I use this one A LOT in Rapaxville.

Personally, I think it should be Alchemists version of heal wounds (and they'd lose access to heal wounds).

I tried adding dispel undead to the cleric's spell list, lol. I don't know how to change the interval though; "only spells with IDs in the interval [0,113] can be used by characters. SO, instead, for that playthrough, I created a ring with unlimited uses. (most playthroughs now, I set the first chest to fit my party)

Whomever has the lowest SP will get the SP from Might to Magic. I usually use it when I know my divinity caster will get the bonus because they're usually needing divinity spell points.

Don't use pray for miracle until the 4th, 5th, or 6th round. Every round adds to the RNG roll.

Yes, Mind Flay (and the other "All Enemies" spells is affected by line of signt; only enemies that are in range and that are in line of sight are affected. Whereas, for Psionic Blast, the group doesn't need to be visible, and only one member of the group needs to be in range. (Yes, that does mean that you can hit out-of-range enemies in the right situation.)

Also, Psionic Blast can inflict insanity, while Mind Flay doesn't have that capability.

There's one spell, Turn Undead, that has all enemies targeting but has only medium range. Holy water has radius targeting and only medium range. On the other hand, there are no cone spells (which are affected by line of sight) that have long range; they're all medium.

I just reply to the post again; if fewer than 10 minutes have passed and no other posts have been made in the topic, this forum will combine the posts.
That's an interesting idea, though I would also give the spell to Priests go give then an Earth realm healing spell that also restores Stamina.

I believe Restore Health is 2nd level, so an Alchemist would not have a healing spell at 1st level. I believe its cost is currently set to 0, which would not work for a castable spell, so I would give it a cost of 5 SP (sum of Heal Wounds and Stamina costs).

I meant, I don't know how you replied to each block separately.

I hadn't considered LoS for all enemy spells. I've definitely wasted SP on that with 1 enemy visible lol.

I checked the CosmicForgeU and Restore Health is a level 1 spell. I added a SP cost and it still won't add it to the possible learnable spells. There are other games (NWN2 for example) that have restrictions on abilities. The restrictions can usually be edited, I just don't know how with W8.