While they havent made an appearance, were also hoping to see Miraidon, Iron Crown, Iron Leaves, and Iron Thorns which comes from Tyranitar
This makes Klefki an ideal counter for fast-paced decks which often make use of Basic Pokmon with Abilities
(compiled from various sources such as TCGPlayer, Collectr, Pricecharting, etc.) If you're interested in the full list of Secret Rares from Mega Evolution Base, you can check them out here
Think of Ace as a slow board wipe tactic that an opponent can only control by using targeted removal on the creature
Most of the cheap cards are the most common to pull in a Booster Pack, so if you don't have one, you likely will soon
The real value here is in that third line of text