Villentretenmerth is another neutral card that can work with all Gwent factions. It has a melee attack rating of 7, which is excellent for a non-hero card. It also has a bonus 'Scorch' effect, which will destroy the strongest enemy melee unit(s), if the total enemy melee score is over 10. If combined correctly with decoys or medics, this card can be used over and over again to maintain battlefield superiority.
The good news about acquiring Villentretenmerth is that it can be obtained from any non-quest related Gwent player in the world. That means any innkeeper, merchant, blacksmith or armorer that plays Gwent could give you this card randomly after you defeat them. It is down to chance though, so you'll most likely need a good few wins before getting the card.