mtg whenever opponent draws card Consecrated Sphinx |4UU| Creature Scrawling Crawler (Foundations Promos)

As the 2nd true flip Planeswalker on both sides (Garruk Relentless into Garruk, the Veil-Cursed was the first), Arlinn offers a lot of options

The key here is not to be purely interactive and reactive, which isn't what you want to do in Modern anyway

1 The Gitrog Monster

Payoffs like Haruspex, Deathbringer Thoctar, Sadistic Glee or Blade of the Bloodchief can even trigger off opposing permanents, which makes them nasty for multiplayer even if your own engine is completely stalled

They also get the more scarce in Magic instances of removing counters or dealing out -1/-1 counters

Magic: The Gathering x Avatar: The Last Airbender Play Booster Pack Not Eligible for Ship to Store This item is subject to the following restrictions: Product ID: 35108305 Avatar: The Last Airbender awaken in Magic: The Gathering