Omenpath Instability is a common Phenomenon card from Black Lotus Unknown Planechase (PUNK), collector number PLA032. Current market price: $19.99, TCGplayer market prices via Scryfall.
When you encounter this phenomenon, each player creates an Entropy enchantment token with "Sacrifice this enchantment: Chaos ensues. Activate only as a sorcery" and an Omenpath enchantment token with "Sacrifice this enchantment: Planeswalk. Activate only as a sorcery." (Then Planeswalk away from this phenomenon.)