Reading a book teaches its spell at level 1, and each further book of the same spell raises it one level, up to 15. Reading one also restores mana equal to the spell's base cost. Every level you know makes the next book of that spell need 20% more Magic (at most 255).
Items with "+ spell levels" add to every spell you cast, and can lift a spell past 15. A spell brought down to level 0 cannot be cast from the book.
Staves and scrolls cost no mana: a staff uses a charge, a scroll is used up. They cast at your own level in that spell, which is 0 if you never read its book, plus your "+ spell levels".
Mana
Each spell's cost drops with its level, never below a minimum (see each spell). Some classes pay a different share of every cost: Rogue × 0.75, Monk × 0.75, Assassin × 0.85; the minimum still holds. The game shows whole points.
Hitting
A spell hits a monster with a chance of Magic + the class bonus − 2 × the monster's level, between 5% and 95% (class bonus: Warrior 50, Rogue 50, Sorcerer 70, Monk 50, Necromancer 70, Druid 60, Assassin 50). A monster turned to stone is always hit. A monster that resists the damage type takes a quarter of the damage; one that is immune takes none (resistances).
Where books and staves come from
The book level and staff level are measured like dungeon depth. Items on the floor and in chests use the depth they lie on, a monster's drop uses half of the monster's level, and Sabine's shop uses the deepest depth you have reached plus 2 (from 6 to 16). A book can hold any spell whose book level is that high or lower; a staff can hold any spell whose staff level is. Three staves in four carry a spell; the fourth gets ordinary magic powers instead.
A book sells for the gold shown with it. A staff gets its charges at random between the two numbers shown.
In town and in other shapes
In Hollowmere only Healing and Identify can be cast, besides the Warrior's and Sorcerer's class skills and the Monk's Search. A Druid in wolf or bear form casts no book, staff or scroll spells. While a Necromancer's Blood Ritual lasts, book spells cost life instead of mana and Healing cannot be cast from the book.
The spell tables assume character level 20 and 100 Magic where those matter. "Raised by the spell level" means the base grows by one eighth per spell level, rounded down each time.
A short jet of fire toward the target: three flames, one tile apart, that burn for 1, 1.25 and 1.5 seconds. Whatever stands in a flame takes fire damage on every tick.
Per tick: (12 × N + 24) / 64, where N is a die of 0 to character level − 1 plus a coin (0 or 1), rolled for each flame. That is 20 times as much per second.
A ball of fire flies at the target and explodes on the first monster or wall it meets, or where its flight ends.
The monster it strikes is hit by the ball and again by the blast; the blast also hits everything in the 3 × 3 tiles around it, except behind walls. It flies faster at higher spell levels.
A burst of light around you. For 19 ticks (about a second) every monster on the eight tiles around you takes damage on each tick, and nothing can hurt you.
X = character level + 1 plus (character level + 1) dice of 0–19, raised by the spell level, then by half again; it is rolled once for the row of tiles above you and once for the rest. Each tick deals X / 64 magic damage, so all 19 ticks deal 19 × X / 64.
While it lasts, the damage you take drains your mana instead of your life. When your mana runs out, the shield breaks and the rest of the blow hits your life.
Each level of it you have read from books (up to 7) also cuts the damage: by 1/21 at level 1, 1/18 at level 2 and so on, up to 1/3 at level 7. Cast from a scroll you never read, it cuts nothing.
It lasts until it breaks or you change level, and it cannot be cast while it is up.
For a while you see monsters in the dark as red shapes: those out of your sight, behind walls, round corners or beyond your light, and those in sight where your light grows faint.
Only those in sight can be picked out with the cursor. It comes only as a scroll, and a Murky Pool casts it too.
Choose a worn or carried item to repair it, for free, anywhere (also in town). Each repair step restores level to 2 × level − 1 durability but permanently takes max(1, maximum durability / (level + 9)) from the item's maximum. Steps repeat until the item is whole.
If the maximum durability reaches 0, the item falls apart.
Choose a trapped door, chest or other object. The trap is disarmed if a roll from 0 to 99 is at most 2 × Dexterity − 5 × depth. You then open the object as usual. It cannot be used in town.
The Rogue also senses traps: a trapped object shows "Trapped" in its name when hovered.
Choose a staff to recharge it, for free, anywhere (also in town). It rolls a strength from 1 to level / the spell's staff level; each step then adds that many charges and permanently removes one maximum charge, until the staff is full.
Sabine recharges staves for gold without lowering the maximum.
The Monk, Necromancer, Druid and Assassin learn five arts each, at levels 1, 6, 12, 18 and 24, without books. An art's level is 1 + (character level − the level it unlocks at) / 3, rounded down, at most 15; "+ spell levels" items and the class items' bonuses add to it. Costs grow with character level, and the Necromancer pays with life. Only Search can be used in town. Each class page has the full rules and numbers by level.
For 30 seconds, monsters within 4 tiles of you take (10 + 2 × art level)% more damage from every source: your blows, your spells and missiles, and your minions.
7 blows, each for (100 + 10 × art level)% of a normal blow, spread over the monsters within 5 tiles that you can see. With fewer monsters, each takes more of the blows.
Raises the corpse of a slain monster within 8 tiles as a zombie (a Drowned Thrall) that guards the spot: it fights monsters near it, then returns. Undead corpses will not rise.
A skeleton warrior (a Grave Soldier) climbs out of the ground beside you and follows you, also to other levels, until it is destroyed. No corpse is needed.
A corpse within 8 tiles bursts. Every monster in the 3 × 3 tiles around it takes 40–60% (+2.5% per level past 15) of the dead monster's maximum life as physical damage, one roll for all of them.
10 + 0.2 per level mana (returning to human form is free)
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Take the wolf's shape: +20% maximum life, +20 to hit, +25% walking speed and quicker blows (an 11-frame attack). Your damage bonus becomes level × (Strength + Dexterity) / 150.
A spirit wolf appears at the spot you aim at (when it is in sight and within 6 tiles; otherwise beside you) and follows you everywhere until it is slain. You can keep 1, plus 1 every 6 levels past 6, at most 4.
15 + 0.3 per level past 12 mana (returning to human form is free)
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Take the bear's shape: +50% maximum life, +(20 + 2 × level) armor, heavy blows (an 18-frame attack) and a 25% chance that a melee hit knocks the monster back. Your damage bonus becomes level × Strength / 75.
A whirlwind wanders toward the target for 2 seconds, or until a wall stops it, striking each monster in its path once for (6–12) + (3–6) × art level + Magic / 8 physical damage.
For 20 seconds a storm rages around you. Every 0.5 seconds each monster within 3 tiles and in line of sight takes (2–4) + (1–2) × art level cold damage and is slowed by 30%.
Only when no monster within 5 tiles can see you. For 13 seconds (+0.5 per level past 1), monsters ignore you unless they stand next to you or you strike them; you walk 20% slower.
Throw a bomb at a spot up to 5 tiles away (it stops short of walls). It bursts over the 3 × 3 tiles there for (7–14) + (1–3) per 2 levels past 12 fire damage, and stuns everything caught in it for 2.1 seconds (+0.07 per level past 12), even monsters immune to fire.
Appear behind a monster within 8 tiles that you can see (there must be free ground behind or beside it) and strike with +30% chance to hit and +120% damage (+20% per level past 26).
The game's spell table also lists Doom Serpents, Invisibility, Rage, Etherealize, Resurrect and Heal Other. No book, staff or scroll carries them in this single-player game.