I have two of the same hero, as I started with one and got another copy of one through using gems. However I can only use one at a time! Why is this? And whay can I do with the other one that I will not be using? Will it just sit there unused
You can sacrifice the lesser hero for the better one. You can tell at their skills to see which is more superior, then sacrifice the other one in your heros alter by selecting the better hero and upgrading his skill.