As competitive Magic continues to embrace the age of Arena, WotC is taking advantage of Commanders popularity in the tabletop space as evidenced by 2020 being The Year of Commander. And the more people get invested, the more people start looking at those old Reserved List staples and licking their lips
Attacking and blocking During your combat phase, you will attack your opponent with your creatures, and they will have the chance to block with theirs
They have no additional abilities, just efficiency
Urtet, Remnant of Memnarch You could pick another 5-color commander with minimal synergies, like Kenrith, the Returned King or even Kyodai, Soul of Kamigawa, but Urtet, Remnant of Memnarch can synergize slightly, especially if you keep Brudiclad, Telchor Engineer and the myr subtheme in the Creative Energy precon (which I wouldnt!)