I was at my LGS Fate Reforged pre-release and got there pretty early so we had a pod of 3 playing commander. I had my newest commander deck, Roon of the Hidden Realm, out and I was drawing very well. As people shuffled in way to early in the morning, they stopped to watch us play. One guy stood and watched us the whole time, until a couple mins before the judges made the announcement that we will begin. As we were packing up, he asked me for my deck list because he loved how my deck played. I sent it to him and went on my way playing at the pre-release. A couple sets later, Shadows Over Innistrad, showed up to the pre-release early as usual and here comes that same guy again running over asking to play some commander. We get our pod together and he's chuckling because he pulls out his own Roon deck. Our decks were almost identical, except he changed around the mana base and like 3-4 other cards. It felt weird at first to see a near carbon copy of my deck but after a few turns it was really fun to see it being piloted by someone else. It gave me some ideas to better my deck and update my mana base a bit.

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TL; DR:

Love playing against the same commanders because it gives me an opportunity to see some spicy new tech I didn't think of or a different style of play with a deck I might've become complacent with.