Some include a physical or vocal component, like Blacker Lotus or the Gotcha! mechanic on Touch and Go, some have rules that specifically reference flavor text or artists, like Carnivorous Death-Parrot and Drawn Together, and some require interacting with people or objects outside the game (Ashnod's Coupon being my favorite)
Troemll, Seymours Butler gives you counters on your team, but where were all pumped is in the tap ability to Proliferate X times, which is kinda insane
can target a creature that's currently blocking or being blocked by a legendary creature, or one that blocked or was blocked by a legendary creature earlier in the turn
All of these aspects come together to create a great portrayal of a Houndoom in natural Pokemon environments, standing proud and likely protecting its territory - just waiting to strike if needed
At the time we went to press, there were still unpreviewed new cards in these decks which are also in the main set, so not mentioning them isnt an oversight