[HELP]How do these mods work?

I have 100% fishing mod from kukulite, but I want to know how the mod work, which means it could be extend to other minigames such as fossil restoration if I undetstand the principle.
Is it possible to modify a certain .dll for minigames just like skill.dll for one-charging FB? If possible, which .dll ?

Well for things such as kukulite you are going to have to code your own, for dlls you'll probably need to find it on your own, almost no one will look for you for free