medal guardian of midgard
 

What does "Battles won using Edda" means ?
I mean, once you've got the Edda skill, you're using it during every single battle. So when a battle is counted as won USING Edda?

And what about the "in the first 6 rounds". First I thought that you must finish the battle in the first 6 rounds, but no, I won a lot of battle this way that are not counted...

It means as you said - you need to choose one Edda skill at the beginning of the battle, and win the battle in 6 rounds. I am only on the first 4 islands, but already have the first level of the medal and am at 40/50 now.

Note that I think it is not win in 6 rounds - it's win whilst Edda is still active so the first level of the medal requires you to win in ?3? rounds.

Hmm, possible...