Eloren Wilds is a common Plane — Shandalar card from Planechase Planes (OHOP), collector number 7. Current market price: $3.79, TCGplayer market prices via Scryfall.
Whenever a player taps a permanent for mana, that player adds one mana of any type that permanent produced. Whenever chaos ensues, target player can't cast spells until a player planeswalks.