The challenge is already done so this thread is kind of outdated but the Wererat Leaders are the new Leader Abilities released during this Year Hidden Cache, Overwhelming Hunger, Mahakam Forge, Imposter, Uprising and Blaze of Glory.
Actually there is an achievement still active that says win 100 with wererat abilites
There are a bunch of other achievements that are very hard to figure out since its not defined in the achievement description. example: win X games with crimson abilities, win X games with thronebreaker abilities.
Crimson Curse
Blood scent
Ursine Ritual
Double Cross
Pincer Manuver
Call of Harmony
Thronebreaker
Deadeye Ambush
Enslave
Fruits of Ysgith
Royal Inspiration
Patricidal Fury
Those expansion Leader skills are usually next to each other in the contacts menu but I guess it was easier to figure out which Leader skill belongs to which expansion before they decoupled Leader skins from Leader Skills, before that you just needed to look into the Reward Book to see that Eldain (Deadeye Ambush) for example belongs to the Thronebreaker Leaders
Thanks for explaining those abilities. I, too, didn't have a clue about them.