Crimson curse was first big expansion to Gwent. We got trailer of it in March 4, 2019 ensuring gamers that new expansion will have 100 cards, so community got excited. Developers had huge opportunity to promote new content during first official post beta tournament, Gwent Open #8 and they used it very well. Day by day cards were leaked by community members and hype was growing. CD Projekt RED was making Leaders Spotlights, same thing they did with Thronebreaker leaders.
New expansion added few new keywords and statuses to the game, we got vitality, bleeding, formation, assimilate, harmony, shield, purify, poison, berserk and deathblow. Each faction got cards for brand new archetypes. For example, Monsters got a lot of vampires with Dettlaff as a new leader for them. Skellige got Svalblod and his Selfwound package.
Expansion has been released in March 28, 2019. Dettlaff quickly dominated meta, few days later Jason Slama, game director, publicized on his twitter that playrate of Dettlaff is higher than they expected and he will get nerfed. In April 4, 2019 developers released hotfix, which had included nerfs to Dettlaff van der Eretein and Dettlaff: Higher Vampire, and new monsters leader turned into unplayable until rework.