Legendary units

heroes with very powerful abilities,You can only put 1 copy of one in a deck, and only one copy may exist at a time.

They might even have a maintenance cost just to keep them in play. Maybe even a high one.

I’m thinking specifically cards strong enough to swing a late game you’ve been losing (if you play them right) or seal the deal much quicker if you’re already winning by a lot.

totally off my head examples:

Salia, Queen of goblins.

cost: 1000 gold, 50 valor

All mortal settlements may produce 2 units within 6 hours.

Every 12 hours pay 500 gold or lose Salia, Queen of Goblins.

Xin, son of the wind

1200 gold 20 Valor 30 mana

All mortal units have their base speed reduced by 1 hour/league

Every 12 hours pay 50 mana or lose Xin.

You get the idea. Super powerful, but hard to get on the field and if you do, theoretically everyone has to kick you resources to keep the card in play,unless it’s end game and you’re already going to win, in which case maybe these guys would help speed up the tedium of “cleanup”