What is your opinion on 'contract systems'?

Personally, I like them, it makes the magic system more interesting and complex. Hence why I added one to mine—heavily inspired by Hunter x Hunter and Chainsaw Man.

In my system, aside from Innate Arts (which are inherent abilities set are birth) and External Arts (which are basically magic spells that can be learned) There exists another system called 'contracts.'

Psychomancers can form contracts with Psychomancy. These contracts can with others, or with oneself.

Contracts made with other individuals are used to establish agreements and terms that have to be honored, otherwise there will be severe consequences (like dying or getting cursed). An example between two characters of mine: "Professor Floxxing formed a contract with the Patriach of House Harrowick. In exchange for sharing his research, the patriarch gave Floxxing pieces of his flesh."

You might be wondering, is there something enforcing these contracts? Making sure they're being followed? Yes, and his name is Gabriel, the King of Oaths. A nigh-omnipotent and nigh-omniscient entity that keeps track of every contract made and ensures their effects.

Now let's move on to contracts with oneself. Psychomancers usually make contracts to boost their abilities, giving themselves a higher advantage, but they must give something up in exhange. An eye for a leg. The greater the cost, the higher the reward.

For example, let me use a few of my characters.

Angela Moreau - Angela's right eye allows her to see into the past, while her left allowed her to see the future. She made a contract with Gabriel, sacrificing all the vision in her right eye which in turn greatly amplified the power in her left, allowing her to see weeks into the future as opposed to just mere hours.

Matteo Zamora - Matteo's contract with Gabriel greatly amplified the potency and destructive power of his fire abilities, to the point of even harming beings with a natural immunity to heat. However, in exchange, the contract made him extremely weak to heat, his own power harming him in the process.

Rey Ishigami - Rey's contract weakened his ability, but in exchange it becomes stronger every minute as long as his target stays in within his range.

Adonis - A contract he made, sacrificing his ability to feel emotions. In exchange, his attacks can now negate the regeneration of an immortal.

Laura Peterson - Innate Art that manipulates gravity. Her contract greatly amplified her ability, but at a cost—she's unable to use her Art, unless within an enclosed space (like a gymnasium)