If you use "Shield & Sword" to switch the original ATK and DEF of a monster and then Tribute it with "Castle Gate", the damage inflicted will be equal to the monster's unaltered original ATK. For example, if you use "Shield & Sword" to switch the original ATK and DEF of "Mystic Tomato" and then Tribute it with "Castle Gate", you will inflict 1400 damage to your opponent's Life Points.
You can Tribute a monster whose Level is reduced to 5 or less by a card effect.
If you Normal Summon "Fusilier Dragon, the Dual-Mode Beast" without Tributes and reduce its Level to 5 or less with a card effect, when you Tribute it with "Castle Gate" you will inflict 2800 damage to your opponent's Life Points (the original ATK of "Fusilier Dragon, the Dual-Mode Beast").
When you Tribute a monster with a printed ATK value of "?", no damage is inflicted to your opponent's Life Points.