Leona, Zealot

What counts as reducing a unit's Might for Ahri, Confident? If I play Discipline on my 1 [M] unit while it's stunned and located at the same battlefield as an enemy Leona, Zealot, will I trigger their Ahri, Confident located at that battlefield?

Reducing a unit's Might means an ability of an object you control causes a unit to receive a -[M] effect. Ahri, Confident will trigger if you Discipline a stunned 1 [M] unit at the same battlefield as an enemy Leona, Zealot.

Although Discipline never causes the unit's Might to increase, the unit goes from 1 [M] with a -0 [M] effect applied to it, which will not trigger Ahri, Confident, to 3 [M] with a -2 [M] effect applied to it. This change in state triggers Ahri, Confident, the same as a 3 [M] unit being stunned and receiving a -2 [M] effect from Leona, Zealot's passive ability. Note that this doesn't work for other cases: if a stunned 3 [M] unit at the same battlefield as an enemy Leona, Zealot has Discipline played on it, that unit will not have a new Might reduction effect applied to it and thus Ahri, Confident will not trigger. Spells, triggered abilities, and activated abilities are easier; if a spell, triggered ability, or activated ability applies non-zero -[M] to a unit, Ahri, Confident will trigger.