Whenever a Pokémon damages 1 of your Pokémon, reduce that damage by 30 (after applying Weakness and Resistance). This power stops working if you have more than 1 Unown M in play. (This power works even if Unown M is Asleep, Confused, or Paralyzed.)
Unown M’s Metal should only reduce damage done to your Pokémon with Unown in their name. Additionally, Metal should still work even if you have more than 1 Unown [M] in play. This disclaimer text was originally intended to simply specify that you can only use 1 Metal Pokémon Power at a time.