Unstable Mutation (ARN) from Arabian Nights, available at 401 Games Canada.

• Rarity: Common
• Finish: Normal
• Artist: Douglas Shuler
• Card Text:
  Target creature gains +3/+3. Each round, put a -1/-1 counter on the creature during its controller’s upkeep. These counters remain even if this enchantment is removed before the creature dies.