Players describe what effect their magic casting will have. GM will determine two things:
Does this casting require a roll? If the answer is yes proceed to #2, otherwise the spell effect happens as player describes
Using the normal Difficulty Scores Guidelines, the GM determines the target for the player to roll. GM can use the target’s DS as a basis if it makes sense to do so. If the situation dictates, the GM may increase this (longer range, trying to change reality, etc). The player will use their ERUDITE class to test for the spell casting. GMs may have bad things happen when casting fails.
Players may sacrifice 1HP for a +2 bonus to their die roll. HP lost due to this can only be healed through rest.
A really dedicated mage can spend weeks prior to adventuring to create a focus (be creative) or totem. If this item is in the mage’s possession when casting the spell, they can add a +1 bonus to rolls to cast spells.