This mod was made with user support in mind, which means adding your own custom syringes is super easy if you know what you're doing.

If you intent on adding your own syringes to the mod, for yourself or as a public expansion, all you need is a little LUA knowledge and that's it, no need for new sprite or XML editing.

You can know all about modding Syringes! in the mod's official documentation: https://github.com/AgentCucco/syringes-docs/wiki

If you have any doubts, feel free to ask in the official Isaac discord at @AgentCucco#6086/@AgentSpoocco#6086 or comment in here, I'll try to be as active as I can!