This is the LEAST achievement of the SUPER7 achievements that you should worry about.
1. complete
Seven Squared achievement that anyways requires you to complete 49 cards
2. Complete other specific achievements that are required to complete a card each
Block-Buster achievementToy Box achievement3. Complete the last 26 cards simultaneously with
High-Roller achievement in order to reach level 10.
It's basically playing new cards that haven't been played in order to receive 5,200XP for completing them each instead of just 200XP for completing played cards each.
With that you'll complete both that achievement and
Magnificent 77 achievement