Vancian Channeling a magic variant

Games like Dungeon Crawl Classic have showed us that the ability to cast spells until some disaster happens are not really unbalancing since the magician and his allies know that each casting could spell disaster.

For my home brew clone project I want a magic system that can be easily added as a variant of the existing rules, something that build on usual rules and at the some time adds what I think is needed.

The mechanics that I want to add to standard "vancian" magic is a roll for each single casting to see if the magic was cast properly or something backfired, at the same time I want to keep all the tropes of the standard vancian system: books, memorization, multiple memorization of the same spell, spell-memorization-table and so on.

To reach this result I am going to introduce the idea that spells are not memorized (and forgotten when cast) but memorization is a lay-men term to indicate something more complex, indeed in this system spells they are some sort of magical non-material constructs that is used to give shape to magical energy channeled by the conjurer from elsewhere; furthermore the act of using the construct to channel magical energy can be damaging to the construct itself (to the point of its utter destruction, exactly as it was erased from existence given rise to the myth of "memorization") so one of the usual result of spell use is the damaging of the construct and some penalty to further use of it. The summoner can repair the spell construct if he has access to his spell books or if he want to repair a mastered spell (more on this later).

It must be noted that spell can be repaired or even constructed from scratch whenever the illusionist want to do it (you don't need 8 hours of sleep since it would have no more meaning in this system), the time to build a construct from zero is (15'xSpell Level), to repair it instead you need (1'xSpell Level) for each point of malus to further castings.

Obviously, given my objectives, the wizard will be able to construct and keep in mind as many constructs as indicated by the standard memorization table of your favorite rule variant (be it AD&D 1st edition, D&D BECM, OSRIC, Labyrinth Lord, Basic Fantasy RPG, Swords & Wizardry, Crypts & Things, Astonishing Swordsman and Sorcerers of Hyperborea, Adventures in the East Mark, Ambition & Avarice..... or whatever system uses spell memorization for most of its classes), the only thing that this system is going to make useless is the "sorcerer" mechanics introduced in same variant like D&D 3rd edition, or the magic systems of D&D Next and ACKS (because they are using a variant of 3rd edition sorcery as the only magic system), but even in this case the system can be easily converted (the ACKS system more easily than D&D Next since it uses standard memorization tables while the Next have a reduced daily usage table and a level based number of spell readable).

When a magic-user want to cast a spell he must make a Channeling-Roll to see how well he managed to channel energy through the spell-construct, the target number of such a roll is modified by the caster level and by the spell level (further modifier can be added by longer casting time, missing components, special focus and whatever - maybe in a future post or in my complete rules, just a few note at the end of the post).

The base target is 14+Spell Level, the roll is modified by the relevant characteristic (intelligence for magic-users, wisdom for clerics) and the character gain a +1 for each 3 caster level rounded down (rangers, and paladins gain a +1 for each 4 level beyond the 9th level in most standard rules). So for example a 7th level magic user with +2 to intelligence want to cast a Fireball (which is a 3rd level spell and the construct was not previously damaged), the target number for this casting is 14+3=17, the bonus of the magic user is +4 (+2 for intelligence and +2 because he is 7th level)

natural 1: spell is not cast, disaster table, backfire and the spell-construct is destroyed

16 or less: spell is cast with some side effect, the spell-construct is damaged (-1d8 to spell-construct and furhter casting unless repaired)

17 or more: spell is cast, the spell construct is damaged (-1d4 to spell-construct and further castings unless repaired)

natural 20: spell is cast with some additional effect (special casting table)

It must be noted that Wizards and Clerics have mastery over 3 spell per level, this are the spell that can be constructed/repaired without a spell book or a mystery book (yes in this system even clerics needs some sort of recording to gain access to their vast repertoire of spells - mystery books work exactly like spell books but are considered holy items).

Will he control his magic?

The tables are for now omitted, but let's consider some guidelines:

+disaster table: should contemplate curse, ability losses, ostile monster summoning, ostile demons/devils conjuration and random magical effects on the caster and/or his allies

+backfire table: lesser magical effects on the caster and/or his allies

+side-effects: additional ambient (lights, sounds, tremors, vapors, smells) effects

+special result table: lessened saving throw, additional damage, additional range or duration some additional effect.

A few suggested spell casting roll modifiers:

add 1 full round/minute to spell casting: +1 (max +1!)

use a special focus (lesser magical item) for that spell: +2

use a generic focus (lesser magical item) for a group of spells: +1

destroy a special material component: +1

don't use a needed material component: -3

don't use somantic component: -2

don't use verbal component: -2

take half casting time: -3

Or maybe it's a +2 focus to the various hand spells

I am adding same optional result tables as options and memos to myself

natural 1: spell is not cast, disaster table*, -2 to all further castings until you are cleansed**  and the spell-construct is destroyed, furthermore make a save for each other spell construct or it's damaged (-5 to spell-construct and furhter casting unless repaired)

16 or less: spell is cast at reduce efficacy***, backfire****, the spell-construct is damaged (-5 to spell-construct and furhter casting unless repaired)

17 or more: spell is cast with no backfire, the spell construct is lightly damaged (-2 to spell-construct and further castings unless repaired)

natural 20: spell is cast with some additional effect (special casting table: double damage, double duration, double save take worst or the like)

In the d20&d12 system this will look like:

f-- (1 on d20 & 1 on d12): spell is not cast, disaster table*, -3 to all further castings until you are cleansed**  and the spell-construct is destroyed, roll a save for each spell construct to see if it's damaged (-5 if save is failed)
f- (fail & 1 on d12): spell is not cast, disaster table*, -1 to all further castings until you are cleansed**  and the spell-construct is heavily damaged (-10 to spell-construct and furhter casting unless repaired)
f (fail & 2 to 12 on d12): spell is cast at reduce efficacy***, backfire****, the spell-construct is damaged (-5 to spell-construct and furhter casting unless repaired)
s (success & 1 to 11 on d12):  spell is cast with no backfire, the spell construct is lightly damaged (-2 to spell-construct and further castings unless repaired)
s+(success & 12 on d12):  spell is cast with no backfire
s++(20&12): spell is cast with some additional effect (special casting table: double damage, double duration, double save take worst or the like)


* this is bad as all the magic channeled goes into an unintended wild magical effect that can alter the local area for a long time (days or weeks) or hit heavily the mage, his allies, enemies or bystanders for a very long time (months or permanent)
** cleansing take off a -1 for each day without using spells and doing some sort of meditation (no other activity is possible)
*** the enemy get double save, or damage is reduced in half or similar
**** some energy goes into a side effect that can hit the mage, his allies, enemies or bystanders... or even some local effect