Helherron Priest Spells
Priest spells are cast by the Priest, Monk, and Ranger.  They are also cast when using an instrument, but you cannot pick which spell is cast then (See the Music skill and the Bard class for more information).  When you cast a spell you select a multiplier to cast it at, the magic point cost (MP) listed is for the multiplier of 1.  Increasing the multiplier increases the MP cost and *may* provide some benefit.  Damage spells increase damage done, healing spells increase hit points restored, summon spells summon more creatures, but some spells seem to be unaffected by casting them at higher multipliers.
I believe this list is complete. However, because of how random spells are, I could be missing something.
Spell	MP	Description
Very Easy
Heal Minor Wounds	3	Heals a small amount of damage.
Light	3	Caster's body starts to shine very bright light making it easier to operate in darkness.
Holy Shield	3	Target's AC is increased by 6 and damage from spells is slightly reduced.
Poison Cloud	4	Creates a slightly poisonous cloud to a 3x3 area.
Dispel	4	Remove all spell effects from target.
Injurious Touch	4	Causes some damage to target.  Base damage 10-30.
Clear Mind	3	Removes confusion(natural and magical) and fear from target.
Cause Minor Wound	5	Causes some damage to target.  Base damage 10-18.
Blur Vision	4	Makes it difficult to hit target with ranged weapons and some spells (darts, bolts, etc…).
Weakness	4	Causes target to inflict lower damage in combat.
Create Web	5	Creates some cobwebs.
Easy
Cure Disease	3	Removes disease from target.
Awaken	4	Wakes up as stunned target.  (Removes stunning, sleep…)
Summon Minor Animal	6	A weak animal is summoned to help the caster in battle.
Weaken Poison	5	Target's poison becomes milder.
Create Wall	6	Creates a brickwall.
Turn Undead	4	Causes a great damage to undead creatures.  Base damage: 35-70.
Transfer	5	Two targets are chosen and they swap positions.
Repel Undead	4	Target repels undead creatures for 5-10 turns.
Bless	6	Target's all weapon skills are increased by 10.
Create Water	5	Creates water to a 3x3 area.
Blindness	7	Target creature is blinded for 5-10 turns.
Anesthesia	7	Target can receive +25% more damage.
Detect Invisible	6	Target is able to see invisible things.  Duration: 5-6 turns.
Haemophilia	6	Target starts to greatly bleed.
Intermediate
Diabolic Afterlife	6	Causes target so that when it dies, it will raise up as an undead and serve the caster of this spell.
Summon Undead	12	An undead creature is summoned to help the caster in battle.
Mana Shield	9	Causes damage inflicted to target to be reduced from his magic points.
Create Great Wall	8	Creates a 3x1 brickwall.
Anti-magic	6	Target's ability to cast magic spells is highly reduced.  Also destroys up to 40% of target's mana.
Blink	5	Target will be teleported to a random location on the battlefield.
Precision	7	Target's ranged damage is increased by 25%.
Heal Serious Wounds	8	Heals a nice amount of wounds.
Levitation	7	Causes target to levitate.
Hard
Summon Major Animal	16	An animal is summoned to help the caster in battle.
Regeneration	7	Target regenerates 2-3 hit points in one turn.
Aural Perception	8	Enables target to perceive creatures' auras.  This vision is not limited by walls or light.  Duration: 5-6 turns.
Paralysis	9	Target is paralyzed for 5-10 turns.
Cause Serious Wound	8	Causes a lot damage to target.  Base damage: 30-55.
Mass Blink	12	All creatures will be teleported to a random location on the battlefield.
Create Great Web	11	Creates a large area of cobwebs.
Invisibility	10	Target is invisible for 5-6 turns.
Greater Anesthesia	12	Target can receive +50% more damage.
Charm	10	Target is charmed for 5-10 turns.
Necromancy	13	Raises up dead bodies as skeletons.
Create Food	12	Creates a nice amount of food.
Very Hard
Mass Haemophilia	14	All enemies that fail to resist start to greatly bleed.
Identify	10	Identifies items.
Uncurse	18	Removes curse from an item.
Heal Critical Wounds	14	Heals a great amount of wounds.
Mass Cure	12	Wakes up, cures bleeding and removes confusion and fear from all friendly creatures.
Mass Heal	18	Heals all friendly creatures.
Divine Light	12	Bright daylight for 5-6 turns.
Cause Critical Wound	14	Causes a great damage to target.  Base damage 60-100.
Mass Dispel	14	Remove all spell effects from friendly creatures.
Mass Wound	16	Causes a slight to most hostile creatures.  Base damage: 10-40.
Resurrect	25	Resurrects a dead creature.
Summon Demon	32	A demon is summoned to help the caster in battle.
Neutralise Poison	12	Neutralises target's poisoning.
Finger Of Death	19	Target dies.
Heroism	40	Target becomes heroic.  His all physical skills (weapon skills, toughness, swimming, etc…) are increased by 50.
Gate Travel	50	Your whole party is teleported to any location.
Summon Golem	90	A golem is summoned to help the caster in battle.
Apocalypse	66	Causes huge damage to most of hostile creatures in battle.  Base damage: 40-390.
Death	34	Target dies.