Inflict 200 damage to your opponent for each card in their hand and for each card they control.
Rulings
Individual Card FAQs
If you activate "Secret Barrel" and your opponent activates something as a chain, the chained card is included in the number (so if your opponent's only card on the field or in his hand is "Mystical Space Typhoon", and he chains "Mystical Space Typhoon" to "Secret Barrel", he still takes 200 damage).
Trap|
Normal