Back when I was watching "Buffy the Vampire Slayer" weekly, there were few television moments more exciting than when that series would crossover over with its spinoff "Angel." Sadly, once the shows were airing on different networks, the events of Sunnydale barely warranted a mention in Los Angeles, at least until "Buffy" was wrapping up its run, but those episodes were fun when they happened. The CW's Arrowverse later became known for its epic crossovers, which attempted to capture the...