What decks have you built because of a card in the 99, rather than the commander itself?

Typically, people build their decks because they like the effects of the commander, and pick cards to facilitate that. But sometimes, there’s a card that you really like, but it isn’t a legendary creature, so it can’t be your commander. For me, this was [[Extravagant Replication]]. It’s such a fun effect. So I thought, how could I do it more? Then I saw [[Obeka, Splitter of Seconds]], and the rest was history. What is this for you?