Teval exacts a toll for casting spells, making it so you lose life equal to its mana value, and thats for everything, not just spells you cast with a delve cost
Below is my favorite Mountain and Forest
This makes it a high-ceiling ramp card in Commander artifact shells like Urza, Lord High Artificer or Breya, Etherium Shaper
While its symmetrical effect is typically seen as a downside compared to Doubling Season, you should instead use its presence on the field to your political advantage: Dont remove me from the game, youre getting value off of my Primal Vigor, Wait, I can cast Primal Vigor next turn and we can swing in with all those Tempt with Vengeance tokens, etc
Seeing as Cube is an amalgamation of some of the best cards in MTG, you can draft some combinations like this that'll win most games straight away: Doomsday + Thassa's Oracle: Get rid of your deck and you win