If you Set “Fusilier Dragon, the Dual-Mode Beast”, even without Tribute, you do not have to show it to your opponent.
If you Set “Fusilier Dragon, the Dual-Mode Beast” without Tribute, it has ATK 1400 and DEF 1000 when flipped face-up.
If “Fusilier Dragon, the Dual-Mode Beast”, with halved ATK and DEF because of its effect, is flipped face-down, and then flipped face-up again, it will then have its full ATK 2800 and DEF 2000.
If you have “Fusilier Dragon, the Dual-Mode Beast” with original ATK of 1400 because you Summoned or Set it without Tribute, and you equip it with “Megamorph”, its original ATK will be 2800 when your Life Points are lower, and 700 when your Life Points are higher.
If you Summoned this card without Tribute, and then “Skill Drain” is later activated, the ATK and DEF are no longer halved. If “Skill Drain” is later destroyed, the ATK and DEF still remain 2800/2000.