When does Assault apply in relation to Ahri Legend's ability that reduces attacking units' Might by 1?

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Accepted Answer

Assault is a continuous bonus that applies while a unit has the Attacker designation. Ahri’s -1 Might to attacking units and Assault both modify a unit’s current Might simultaneously; when you sum Might for combat (and when checking whether a unit is killed), include both effects together.

Assault applies as part of the unit’s current Might once the unit has the Attacker designation. Ahri’s -1 to attacking units and any Assault bonus are combined into the unit’s current Might when you evaluate and sum Might for combat damage and lethal checks.

A unit gains the Attacker designation during Combat; while it has that designation it has any Assault printed or granted to it [807.1.d] [807.1.c]. Continuous effects that modify Might (for example, Ahri’s -1 to attacking units) are also active while the unit is an attacker and change the unit’s current Might [710]. At the Combat Damage Step you sum the current Might of all Attacking Units; that current Might includes both Assault bonuses and Ahri’s -1 (netted together) [460.2.a] [807.2]. Use that net/current Might to assign and deal combat damage and to determine lethal damage and kills [143.2.a] [143.2.b].

If the combined effects reduce a unit’s Might below 0, treat its Might as 0 for purposes of summing and assigning combat damage [143.2.b]. If Assault is granted or removed during combat (for example by a spell or ability that takes effect after attackers are chosen but before damage), the unit’s current Might is recalculated and the new value is used when you sum Might for the Combat Damage Step [710] [807.2]. If Ahri’s reduction is implemented as a one-shot triggered effect rather than a continuous characteristic (contrary to our assumption), the timing of that trigger relative to when Assault becomes active could change the numeric result; see assumptions.

Assault is not an effect that waits to 'apply later' — it is a continuous characteristic that grants +X Might while the unit has the Attacker designation [807.1.c]. A static or continuous reduction to attacking units’ Might provided by Ahri also functions as part of the unit’s current Might while that unit is an attacker [710]. During the Combat Damage Step you "Sum the Might of all Attacking Units" using their current Might [460.2.a]. Because both Assault and Ahri’s -1 are continuous modifiers to Might that are active while the unit is an attacker, they are netted together when determining the unit’s Might for combat; in other words Assault is included in the same "current Might" calculation as Ahri’s reduction [807.2] [710]. Finally, that net Might is what you use to assign and deal damage and to check for lethal damage (and if the result is negative it is treated as 0) [143.2.a] [143.2.b].