I'm not sure if you have seen the custom weapons used in SpeedSilver's YouTube videos (Video i'm referencing: link) but something like that so when you kill with it, it increases in the level of sharpness by one or you gain a permanent heart or a staff that gives you a random amount of emeralds for each entity you kill.
Hello! I've recently started modding and i'm not amazing so i'm not too sure where to start with this if someone could help by replying with some good resources or something i can use to learn that would be amazing :)