I tought the exact same and in fact... I also did implementa it. At the beginning it was working correctly and I had water bullets going trough fire enemies while wood bulletts didn't even destroy them... but for some reason after i added all enemies and all bullets (and all the code)... it just stpped working. Theorerically the code for it is there.. it just does not work... and I had no time to find out why during jam time:(