New clerical monster spell (possibly also a player spell) that creates a region of black storm clouds between the caster and target and moves across the map towards the target. The clouds block vision, can strike anything in or near them with lightning (though not intelligently), wet items on the floor beneath them and in the inventories of monsters beneath them, hit things with gusts of wind if those are implemented, and can spawn temporary lightning monsters that vanish when the cloud does.

Another variant of this idea is as a static cloud that can be targeted like a stinking cloud, probably as a level 7 spell (depending on how bad the lightning is).

A new spell that is primarily a healing spell, but is in the clerical school instead of healing and works by divine influence, which would make priests and knights good at casting it, but not healers and wizards.

A monster spell ‘curse weapon’ or ‘curse equipment’, a clerical spell that is a weaker version of curse items: it only curses one item, but selects from among worn and wielded objects. If the target isn’t wearing or wielding anything, it will target one piece of equippable gear from their inventory, or failing that a random item.

Move the spell of light to the clerical school.

Spell of necromancy that turns a corpse you’re standing on (or possibly adjacent to you) into a tame undead. Probably in the clerical school, though a case could be made for matter (and certain variants have a school of necromancy which this would much more directly fit into). It will work on corpses of undead that you have killed. Casting this spell would have some sort of penalty for lawfuls; there would be some sort of warning before trying to cast it.

You can normally only create zombies or mummies when an undead monster exists for the kind of corpse you are animating (i.e. a jackal can’t be turned into undead but a gnome can turn into a gnome zombie/mummy). For intelligent monsters that have no counterpart, the spell can create ghosts.

At a high enough skill or caster level, you can create skeletons from the corpse of any vertebrate, and maybe even vampires from humanoids. You can also create wraiths and shades from monsters that have no undead counterparts.

Additional clerical spells for aligned priests to cast: raise undead, floor to lava, ball lightning (not a ray and thus not reflectable), summon elemental.

Reduce the level of create familiar significantly, and make it only able to create replacement pets and possibly similar low-difficulty monsters, and not work if you already have any pets. Add a 7th-level clerical spell, “create minion”, that summons tame/allied minions of your god.