Free-form Spellcasting

Magic in D6 Dungeons is entirely free-form; there are no spell lists. You simply declare what you want to do and the narrator sets a difficulty for it. Certain situations and conditions might increase or decrease the difficulty, though. There are other things to consider when casting spells, too. Casting spells quickly and safely requires three different skills, so it's a heavy investment for those wishing to diversify.

Types of Magic

There are two types of magic: arcane and divine. Arcane magic is the volatile and unpredictable energy flowing through the universe, which talented mages are able to use it to produce wondrous and devastating effects. Divine magic comes either directly from a deity or emerges spontaneously out of mortals who exemplify certain ideals. Arcane magic can produce a wide variety of useful effects, though it can never be used to heal. Divine magic, on the other hand, can never be used to cause damage unless the target is undead.

Casting a Spell

To cast a spell, you must attempt at least one roll, either spellcraft (for arcane) or religion (for divine). To cast a spell as one action, you must succeed on intelligence (for arcane) or wisdom (for divine), otherwise your must spend an entire round casting, finishing with your next action. If you suffer a wound while casting, the spell is disrupted and doesn't work. 

If you fail the roll to cast the spell or are disrupted by taking damage, you must roll awareness (for arcane) or willpower (for divine); failure means you lose your next action and suffer backlash (for arcane) or disfavor (for divine) for the rest of the scene. Failing a spellcraft roll to cast a spell while suffering from backlash results in an automatic wound, which cannot be resisted with fortitude. Failing a religion roll to cast a spell while suffering from disfavor gives you disadvantage on all rolls and prevents any divine casting for the rest of the scene.

It is usually not a good idea to try to cast spells while being threatened by close enemies or you are otherwise in immediate danger of being attacked. Wearing heavy armor or using a shield gives you a disadvantage on awareness and spellcraft rolls, and wearing light armor causes a disadvantage on spellcraft. Attempting to cast a spell without the proper implement causes disadvantage on spellcraft and religion.

In general, a spell with a difficulty of 3 (the lowest difficulty of spell) doesn’t really do anything special, just a very minor effect like lifting a tiny object, creating just enough light to see what's nearby, or making food taste better. Spells that deal damage must meet the difficulty of the target enemy, while those that increase the duration, area of effect, or other factors must achieve an even greater result. Spells that deal mental damage or get around normal defenses (poison gas, etc) should always be higher difficulty. Spells that benefit from environmental situations have lower difficulties, such as calling down lightning bolts out of thunderstorm or summoning a swarm of bats while exploring an underground cavern.

Beyond causing or curing wounds, spells can have just about any other effect, though more powerful effects should require a higher difficulty. Some very powerful spells (teleportation, raising the dead, causing an earthquake, etc.) might require specific artifacts, time-consuming rituals, and/or consumable materials like expensive gemstones.

Arcane
Roll intelligence to cast with one action (otherwise next round), then spellcraft to cast the spell, then awareness on failure to avoid losing your next action and suffering backlash. Can never be used to heal.

Divine
Roll wisdom to cast with one action (otherwise next round), then religion to cast the spell, then willpower on failure to avoid losing your next action and suffering disfavor. Can only cause damage to undead.

Guidelines and Examples

While a free-form spell system can be daunting at first, it's much more liberating as the game progresses. To get you started, here are some sample spells to help establish guidelines for what's possible at each difficulty. Note that these are merely suggestions and the actual difficulty can change depending on many factors, from degree of preparation to environmental circumstances.

Divine Judgment (divine) Enemy Difficulty, gives one nearby undead target disadvantage for the scene 
Smite Evil (divine) Enemy Difficulty+1, causes 3 wounds to a nearby undead enemy
Turn Undead (divine) Enemy Difficulty+2, causes 1 wound to all undead nearby of equal or lesser difficulty
Destroy Undead (divine) Enemy Difficulty+3, instantly destroys one close undead enemy

Electric Jolt (arcane) Enemy Difficulty, causes 1 wound to a nearby enemy
Icy Ray (arcane) Enemy Difficulty+1, causes 1 wound to a nearby enemy and gives them disadvantage
Blinding Beam (arcane) Enemy Difficulty+2, causes 1 wound and disadvantage to an enemy far away
Fire Ball (arcane) Enemy Difficulty+3, causes 1 wound to a target far away and all nearby it of equal or lesser difficulty

Arcane Shield (arcane) 4, negates the next wound the caster suffers during the scene
Healing Hands (divine) 4, heals 1 wound to a touched ally

Lesser Teleport (arcane) 5, move twice instantly
Divine Protection (divine) 5, allows one touched target to roll fortitude to avoid damage

Force Blast (arcane) 6, moves all close targets away and gives them disadvantage
Turn Undead (divine) 6, no undead may move close to the caster

Feather Flight (arcane) 7, the caster can fly for one scene
Battle Prayer (divine) 7, all nearby allies gain advantage on attacks during the scene until wounded

Greater Teleport (arcane) 8, transports the caster and all close allies anywhere previously visited
Restore Health (divine) 8, heals all wounds to a touched ally and restores consciousness