What do you all think about "The Ring Tempts You" mechanic?
I think it's pretty neat, at least from a commander perspective. Making non-legendary creatures into legendary creatures can add some cool synergies with cards like Ratadrabik of Urborg.
It does cool things, but it's definitely a "Mark Rosewater designs a perpetual card that stays on the side" design. Like dungeons, attractions, day/night, etc.