Gandalf the White, for example, is designed to mainly care about legends, but he can also break the famous artifact Isochron Scepter, as noted in this Reddit thread where users recognized the potential that Gandalf's ability adds to the Isochron Scepter
Have I missed any key cards
Last but not least, Commander might be all about your leader, but RPGs are often about your party as a whole, and WOTC wont leave the supporting casts of these games hanging
Like kicker and cycling, its a deciduous mechanic: Magic designers use it when needed , and its not necessarily in every set, or a set's main mechanic
As for the best of the new creatures, O'aka, Traveling Merchant turns your excess counters into carddraw, and Maester Seymour grows creatures of your choice as you grow him