Here is the full list of all 10 Runes of Brennos achievements.
Play for five hours.
Discover and perform the Absorb combo.
Unify Gaul under your dominion.
Perform the Elemental Shield combo.
Perform the Elemental Rage combo.
Perform the Energy rune combo.
Fight 100 rune battles.
Win 30 rune battles.
Win 100 rune battles.
Finish your druid training.