Help with new character class idea

[Thrasher92]

I'm working on making a new character class off of an idea that my friends were throwing around.

What if you had a character that learned spells based off of the enemies it defeats?
For instance, if a creature killed a giant spider and "absorbed its essence" or something it could learn the Web spell.

I was thinking of basing it off of the Dragon Sorcerer but letting it learn spells specifically off of the enemies they fight and as they level up they can choose certain aspects of the monsters to emulate, like how the dragon sorcerer becomes more draconic.

Is this a bad idea? Any tips on how to keep this class balanced but still give it cool features?

[nickl_2000]

This actually sounds like a Wizard reflavoring to me more than anything else. Instead of being able to script spells to their spell book they can perform a special ritual on a dead body to consume and trap some of it's spirit into a necronomican type book. That ritual has a cost in special herbs (the same as the cost of scribing a spell in a book), and takes as long as scribing the book. Also, it can be done with tokens from the defeated monster so that the wizard can do it during their free time.

If reflavoring makes it to easy to get normal wizard spells into the book, then you write a subclass. My own reading of Wizards goes like this.
2nd level - You get a combat type ability
2nd level - You can scribe from animal remains to add new spells to your spellbook.
6th level - Typically something not as directly related to combat
10th level - Helps in combat
14th level - Often a boost to a previous ability or other combat style feature.

[Man_Over_Game]

The problem with an idea like this is the amount of lookup it'd require. Moon Druids, for example, have a very specific list that they can review. However, what you're describing is specific to any creature, of a list of creatures that may or may not get constantly updated. It also incentivizes MurderHoboIsm, as you're permanently rewarded for killing things.

My recommendation would probably be something along the lines of killing a creature of a specific type, then gaining a spell for that specific type of creature, all based on a list of possible creature/spell combinations. When you kill another creature, you can choose to gain its special spell, or keep the one you already have.

So, for example, Spider creatures would have you learn Web, and give you one free casting of Web for the next hour. Killing a Fire Elemental would give you a free casting of Fireball, etc. You unlock higher tiers for your list as you level up, granting higher level spells and higher level monsters.

It'd require some DM ruling, as some creatures might be defined as different types. Like, is a Skeletal Dragon a Skeleton or a Dragon? Best keep the classifications broad.

[Mortis_Elrod]

This seems weird. Youd have to make tables for every monster and have a spell tied to it. Unless you're saying only creatures with spell abilties? well then you're kind of asking the DM to tailor things even more for you.

What would the subclasses be like? what the flavor here?

Just seems loose and formless. Flesh this out more. I would recommend working on the flavor side of things first, and then adding in mechanics that support that flavor.

[Vogie]

I remember making a sorcerer metamagic that would allow you to learn spells that you used dispel magic or counterspell on.

Another option is that it could be a Volo-esque wizard in a low-magic world who would hunt down monsters to study, and base their spells off of beasts and monsters they find.