I'm thinking some sort of Battle game, one v one or team v team, so that it's easier to get drama out of. Let me dig up some notes, and I'll edit this post with my ideas for something.
EDIT:
Concept
You and all other players have access to a special kind of magic, manifesting from your very soul. You duel with other users of the magic to destroy theirs, summoning creatures and casting spells using that energy to break through their defenses, and eventually defeat them. There's a mythological theme, but I'm taking that to include more "modern" mythologies, such as cryptids and conspiracy theories.
You have a deck of (40-60?) cards, one Heart card, and 100 Soul. You play cards other than your Heart by paying Soul for them, and Soul is also your life. To stop spam of high-cost cards being all that matters, you also have a Siphon value. Every card has a Siphon value, and the Siphon of all your current cards combined is the most you can spend in a round. Your Heart card starts in play, giving you a minor ability (for instance: "Pay 5 Soul to draw a card" or "You can pay 2 more soul when casting a spell to deal 2 to target creature" and so on) and your starting Siphon value (3?).
Cards are generally split into four factions:
After World: These are your death gods, spirits, undead, and similar creatures of the night. They drain life and power from your opponents, crippling them to prevent a solid offense. However, they are fragile and a good hit will give them a black eye they won't easily recover from.
High World: The mighty gods, angels, and other such holy creatures have come to purge the land. They hit hard and fast, with lots of destruction effects and high power. They lack staying power, and weathering their assault can leave them open for a finishing blow.
Natural World: Humans and creatures of earth dwell here. They create, buff, and heal, generating more easily than destroying in order to outlast your opponent. They're slow to start up, and if they're blindsided by the opponent, they can fall before they have the chance to lay a foundation. They're not helpless in the early game, with some cards for stalling and defense, but still are weak to the fastest decks.
Hidden World: Aliens, Illuminati and Replicants, all the shadow puppeteers of the world. They employ weird effects to control the board, preventing, obscuring, and complicating your opponent's way to victory. Shadow Puppeteers work in the shadows as their name would suggest, and so are bad at direct combat if the opponent can get through their tricks.
A deck can only have one faction in it, as the soul identifies with one faction only.