When I saw "expensive", I thought of expensive mana costs. So, I wanted to tie a mechanic to paying expensive costs. But what was expensive? Well, since Limited is the most restrictive format in this regard to design for, and assuming this mechanic would be for a standard-legal set, I wanted to make sure to care about what would be "expensive" for Limited. But what is that number? To determine this, I took to polling Twitter:
I only let the poll go for four hours before making a decision, as I needed to write the post you're reading now at the time I'm writing it. But it seems clear 7 is when spells are "expensive" in Limited. From seven, I thought of "lucky number seven." So, I chose to just focus on the number seven and not just "seven or more."
The mechanic ensures you have luck counters placed on permanents, of which many different applications of said luck counters can be applied. In today's card, I chose to design the potential penultimate card, make it a little easy to get rid of, but also make it a legendary creature to be used as a commander, in the colors of which previous cards using luck counters can be included in the deck of. Both Chance Encounter and As Luck Would Have It are alt-win condition cards that use luck counters. And Gemstone Caverns also uses a luck counter.
(I'm always on the lookout for potential "Commander design space" whenever opportunity arises, even in these theoretical situations, to train myself to not miss that chance, or else you get a situation where you miss a legendary werewolf for original Innistrad block.
Keep in mind that Scourge was a set that cared about converted mana cost six or more, and it was in a block that had cycling - so the potential Limited environment would probably also have ways to include seven-cost cards in addition to your cheaper cards with seven-costed abilities.
