Withering Wisps is a uncommon Enchantment card from Ice Age (ICE), collector number 168. Current market price: $0.36, TCGplayer market prices via Scryfall.
At the beginning of the end step, if no creatures are on the battlefield, sacrifice this enchantment. {B}: This enchantment deals 1 damage to each creature and each player. Activate no more times each turn than the number of snow Swamps you control.