Once per turn, you can toss a coin and call it. If you call it right, inflict 1000 damage to your opponent. If you call it wrong, you take 1000 damage.
Rulings
Individual Card FAQs
If you call the coin toss wrong for “Abare Ushioni” you can still prevent the damage with “Pikeru's Circle of Enchantment”, etc.
You cannot chain “Barrel Behind the Door” to the effect of “Abare Ushioni” because you don't know yet if you will take damage or not from the effect.