These are called Regulation Marks
They offered incredible cost-based removal, but the cost of activation meant you will be playing on the backfoot when comparing hand sizes
Here are some options that come to mind: Chain something to s ave 1 monster by changing its Battle mode An example of this is Book of Moon , a Quick-Play Spell
Though the release schedule and product ranges for TCGs can sometimes feel relentless and difficult to keep up with, Fantasy Flight and Asmodee have shown remarkable restraint with Star Wars Unlimited, with a steady pace of sets being released and just one type of booster pack needed to keep going with playing, no matter how you intend to proceed
That's kind of ridiculous if you take it at face value, but there's also the option to create near-infinite loops with self-bouncing creatures like Whitemane Lion and Kor Skyfisher
Maybe the connection is a creature type, or the cards play well together, or they have some story element in common