If the Defending Pokémon tries to attack during your opponent's next turn, your opponent flips a coin. If tails, that attack does nothing.
If the Defending Pokémon doesn't have a Char counter on it, flip a coin. If heads, put a Char counter on it. A Char counter requires your opponent to flip a coin after every turn. If tails, put 2 damage counters on the Pokémon with that Char counter. (Char counters stay on the Pokémon as long as it's in play.)
Be careful if it turns its back during battle. It means that it will attack with the fire on its back.
This is the only card in the TCG that can inflict the Char condition, which served as the precursor for the Burned condition later introduced in the Expedition Base Set. The primary differences between the two are that Char doesn't count as a Special Condition, and it remains on a Pokémon even while Benched.