The first great building of the Oceanic Age was the Atlantis Museum. However, what's considered a skill? Nothing in the official wiki entry for this building refers to a skill. If you're referring to boosts, there are two of them: "Goods Production" and "Plunder and Pillage." Although, "Goods Production" is listed first, I'm guessing you are actually looking for "Plunder and Pillage," as it's the first unique boost for great buildings of this age.
In the future, please be more specific on your clue verbiage.
The Kraken is a new Great Building that comes with a new skill: First Strike.
At the start of the next several fights, there is a chance a unit from the enemy's defense army will be killed immediately. This only applies to the first wave of a battle.
On top of the First Strike skill, The Kraken will also produce Forge Points.