Finishers like Overrun, Titania's Command, and Return of the Wildspeaker close games in one ferocious charge
The planeswalker commander is an amazing card for artifact decks both from the command zone and as part of the 99
There are some scary ones like Walking Ballista, tricky ones like Luminous Broodmoth and the one-sided board wipe Damning Verdict, and each cares about counters in a different way
When you pair it with something like Pitiless Plunderer or Ruthless Knave, you can start looping squirrel and Treasure tokens endlessly
If a permanent has +1/+1 counters and -1/-1 counters on it, they're removed in pairs as a state-based action so that the permanent has only one of those kinds of counters (or none of either kind of counters) on it
whereas, Doubling Season only doubles things for you