If Sett Brawler spends his buff (decreasing his Might from 5 to 4) to increase his Might to 8, does this trigger Fiora's Legend ability which triggers when a unit becomes Mighty?

Ruling: Yes, this triggers Fiora's Legend ability.

Sequence:

• Sett pays the cost of his ability, reducing his Might from 5 to 4 (ceasing to be Mighty)
• The ability resolves, increasing his Might to 8 (becoming Mighty again)
• Fiora's Legend ability triggers when Sett becomes Mighty