I had always wanted to create my own items in BoI, and when Afterbirth+ came out, I decided to do so.
The first mod I made, called "11 new items", can be found on steam here.
As its name says, it adds 11 new items to the game. It also adds 2 new trinkets. All their effects can be found here.
Since it took me about 6 months to design and actually implement all the items, I was pleased by the good reception that it got once it came out.
While creating my first mod, I needed to debug lots of things. I decided to create a debugging tool and shared it with others here.
This mod is incredibly useful to debug enemy states, sounds playing, or just global game information (room indexes, curses...).