Stats handler that allows the use of items to affect it

I am looking to create a form of stats handler that works in an incremental fashion, where each item that you collect will be added to the total of that stat. This would come in three forms

  • Pure - The Value is directly added onto the base stat
  • Multiplier - The Multiplier value multiplies the total of the pure and base stat
  • Set - The base stat is changed directly, before the pure and multiplier

It would be similar to a card systems - Like Rounds - except you would have to apply your values before you go into a fight, so like Warframe (for those of you who know). I have tried so many attempts but do not understand how modulescript handlers should work, and how to give the desired outcome.

Any help would be greatly appreciated.