Does playing a 4 Might unit to Trifarian War Camp trigger Fiora's ability that requires a unit to become Mighty?

Ruling: No, playing a 4 Might unit to Trifarian War Camp does not trigger Fiora's ability. The unit is Mighty from the start when it enters the battlefield, so it never becomes Mighty while on the battlefield.

Sequence:

• When a unit is played to Trifarian War Camp, it gains +1 Might as it enters the battlefield
• A 4 Might unit becomes 5 Might immediately upon entering
• Since the unit is already Mighty when it appears on the battlefield, there is no moment where it becomes Mighty
• Therefore, Fiora's trigger condition (a unit becoming Mighty) is not met

Nuances:

• Moving a unit from base to War Camp would trigger Fiora, because the unit is already on the battlefield when it gains the Might buff
• Playing a unit whose Might increases due to a conditional passive ability (like Shen when defending) would trigger Fiora but not Volibear
• Playing a 4 Might unit to War Camp triggers Volibear (which cares about Mighty units being played) but not Fiora (which cares about units becoming Mighty)