I think many just say here about the Dragon City guide and how amazing and vast it is, but I say it would be nice if I would write here, right from my own experience, which elements damage more which.
Let's begin with the SEA attack. It logically defeats the dragons with the first element as FIRE. Another 'elements' that receive criticals are WAR & ELECTRIC.
Ok, now it's FIRE's turn. It gives critical to the dragons with SEA or ICE as first element.
Third is TERRA which follows the same idea but gives critical to 'DARK' & 'NATURE'.
- ICE -same story- NATURE & WAR;
- ELECTRIC -_- METAL & FIRE;
- DARK-_- LIGHT & METAL;
- METAL-_- TERRA & ICE;
- LIGHT-_- DARK & ELECTRIC;
- NATURE-_- DARK & LIGHT;
- WAR-_- TERRA & SEA.