[LotFP] Opinions needed for Elven magic

FORGET THIS CRAPPY POST AND GO TO THE LINK INSTEAD:
http://www.lotfp.com/RPG/discussion/topic/503/help-me-make-elves-different-from-magicusers-random-table-time/

THIS POST SUCKS... IT'S TL;DR AND THE IDEA ISN'T AS CLEAR AS IN THE FORUM POST I MADE AT LOTFP.

But why don't I just delete this? This is a reminder for self how not to suck.

Elves cast spells like Magic-Users but I want a difference there. If you are familiar with D&D 3e Elves would be more like Sorcerer class in their magic using abilities, but not quite.

This is the idea I am thinking. Magic-Users will be by the book, but Elves will be different. This is how Elven magic works.

Background

Elves have magical abilities. Not studied and learned like Magic-Users with their arcane knowledge, researches and spell books. Elven magic is innate power and more powerful Elf is more powerful his magic is.

Elven magic is chaotic in nature and no Elf can possibly know what kind of powers he will conjure later. Magic is Elves birthright but the nature of it is unknown until discovered.

Elf Spell Progression

Elven spell progression is by the book, but they don't need spell book. Their spell powers come inside them.

Every level when Elf gains new spell slots roll randomly for appropriate spell level new spell slots are gained. Those are the spells Elf can cast. He memorizes spells normally by meditation.

For example if Elf can memorize two one level spells and one second level spell per day that's also the number of spells Elf knows. Roll randomly for two first level spells and one second level spells, those are the spells Elf knows. Elf can memorize spells as Magic-User, for example taking same first level spell twice.

Does this make Elves less capable of Magic-Users? Yes, as they don't have a spell book they can write new spells when they find those. But Elves can still use scrolls, wands and staves normally. But this makes Elves different from Magic-Users as Elves are also capable as Fighters.

The trick is that when Elf casts a memorized spell roll d20 under his level-spell level (1 minimum). If the result is a success, the spell is not forgotten and can be re-cast.

Example:
Tremwel 10th level Elf casts 2nd level spell. He rolls d20 against his level - spell level (8). If the die result is 1-8 he doesn't forget the spell and can re-cast it later.

But as Elven magic is chaotic in nature there's 5% change (result 20) that something goes wrong and the spell effect backfires. For example Sleep spell affects the Elf himself or the fireball blows in front of the Elf damaging him.

It is player's choice to cast spell with this risk. Otherwise Elf cast his spell normally without a die roll and forgets it. There's 5% risk when trying to cast without forgetting the spell, that something goes wrong. Elven magic is chaotic in nature and wild so trying to "tame" the spell when casting it (trying not to forget it) is risky business.

Other option to make spell casting more wild and chaotic is to ignore Elf's level altogether and just roll d20. If the result is same or less than spell level, it fires back to the caster.

Example:
Anwylen 20th level Elf casts 9th level spell trying not to forget it in the process to be able to cast the same spell later. There's 9 in 20 change that the spell backfires harming the casting Elf.
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This is something I try to work out to not make Elven casters weaker and trying to make Elven magic more wilder and chaotic. I am not yet sure how to do it, but this is one option.

Do you have great suggestions to make Elf different from Magic-Users?