Several potential additions for the clerical spell school:

• Bless: this could either be a low-level spell that works like it does in D&D where it gives you a to-hit and damage bonus, or it could be a high-level spell that blesses an item. Possibly it could bless items when cast at Skilled or above.
• Sanctuary: a medium-level spell that effectively makes monsters treat the 3x3 area around you like a coaligned temple for a limited time, unless you take a hostile action which ends the spell.
• Command: Drop: forces a monster to drop its weapon.
• Inflict Wounds: medium-level spell that deals damage while being in the clerical school. Damage should probably scale with skill.
• Hold Person: paralyzes a monster (or more strictly, a humanoid); fits right in since enemy priests can already cast this.
• Silence: Temporarily stops a monster from reading a scroll or casting a spell. Not specified if this should be a debuff or create a region of silence.
• Dispel Magic: Removes magical effects from a monster or multiple monsters. May be of limited use unless added to a variant where monster magic buffs are significant.
• Freedom of Movement: Grants temporary intrinsic free action, allowing you to free up a ring slot.

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.