The Magic system of Shadowfall, is fairly straight forward. You have 100 Mana, and you cast a spell, expending as many points as you want into a spell to have that direct effect (25 Points of Mana Spent on a Heal will heal 25 points, for example). However, Mana, like HP, does not passively regenerate, and can only be refilled by a good nights sleep (Mana Refills during 8 hours of rest, and only by half for 4 hours, etc).
Magic gains no bonuses towards casting, no matter how proficient someone may be. On top of this, mana is spent in increments of 5, and is stable only to 15 points. On the 20th point of mana used, the caster recieves a -1 to hit, -2 at 30, -3 at 40, etc. So while it may be tempting to nuke someone with 100 points of Mana for the whole "FUCK YOU GET REKT!", you're casting at a -9 to your roll (even natural 20's, sorry, no crits).
Thankfully, healing and support spells do not require a roll to determine if you hit or not. Keep in mind you'll want to ration yourself out, between healing, damage, and support.
Available to Hunters and Witches, Hunters require a Silver Crucifix, Witches an Oak Staff
Heal – Base Cost: 5MP, heals target by amount of Mana spent.
Cure – Base Cost: 25MP, cures target of a status ailment.
Flash – Base Cost: 15MP, attempts to blind nearby foes. -3 to Foes Attack on successful roll of 13 or higher. Cannot be amplified.
Concuss – Base Cost: 25MP, attempts to knockback foes, while dealing 1d4 damage on successful rolls of 13 or higher. Can be amplified to 1d8 Damage for double the cost and -3 to attack roll (base cast is -1).
Exclusive to Witches, must have an Obsidian Knife and Golem Heart
Barrier – Base Cost: 15MP, project a 5×5 foot barrier of stone before you or a party member. Barriers have as much HP as you pour MP into them, and cannot be missed by enemy attacks.
Golem – Base Cost: 30MP, summon a Golem from the earth to fight for you, for 1+1d4 rounds, +1 round per 10 additional MP spent. Golems have an AC of 15, attack of 1d8, and an HP of 30, regardless of MP spent.
Golem of Earthen Skin – Base Cost: 60MP, your Golem now surrounds your body as a second skin, shielding the witch for 1+1d6 rounds, +1 round per additional 10MP spent.
Wild Roots – Base Cost: 15MP, attempt to surround and bind a foe in place for 1d4 rounds, on successful rolls of 10 or higher. Lesser Foes are considered "Helpless" if bound, and may be given a coup de grâce.