Mana Cache is a rare Enchantment card from Nemesis (NEM), collector number 92. Current market price: $0.74 (foil $7.02), TCGplayer market prices via Scryfall.
At the beginning of each player's end step, put a charge counter on this enchantment for each untapped land that player controls. Remove a charge counter from this enchantment: Add {C}. Any player may activate this ability but only during their turn before the end step.