It is so rare because it was only printed once
The trailer was a mad riot of colors and particle effects, so while the video above will give you a good idea of how each card will actually play in the TCG, below we've included these stills of the Japanese cards, where it's much easier to actually make out the art
Based on the amount of mana you spend you can choose one tier of spell in this case Fire, Fira, or Firaga to generate a more powerful effect just like you would in the video game
there are only so many more keywords you can add to the deck, so you can only really improve its consistency by adding more ways to bin creatures for Kathril, Aspect Warper
They reward you for having a powerful creature in play by letting you get even further ahead
With how small windows of opportunity are in cEDH, one turn is often all it takes to get there and win especially when the extra turn you take can be between two opponents turns oh yeah, its an instant