However, there are three big reasons that isn't quite true
For its low cost, it does a lot, making it a great fit in both Punk Hazard and Straw Hat Crew decks
Its frill inspired the design of efficient aether collectors
While both Phyrexian Arena and Hypnotic Specter have the potential to see play in multiple archetypes, maybe the most fun way to play these cards is to toss them all together into a Mono-Black Control shell, with Hypnotic Specter being a living x-for-1, Phyrexian Arena being an insane source of card advantage, and Tendrils of Corruption being a solid removal spell that also helps to ensure we don't accidentally die to our own Phyrexian Arenas
Cards in hand are counted after lands have been sacrificed, and creatures on the battlefield are counted after cards have been discarded
You can also help speed this along with similar Dimir creatures like Vohar, Vodalian Desecrator or Obsessive Stitcher