vampire hexmage level up rules Ikiral Outrider power toughness attacking magic

[Crocodile]

if a level 1 Ikiral Outrider attacks me and I sac vampire hexmage to bring it to level 0, how much damage does the Ikiral Outrider deal? (Because I remember some things you cant change once attackers have been declared is the Power/Toughness one of them?)

[Arix]

Power/toughness can change after a creature has attacked. Power is only checked when combat damage is assigned. If it changed before then, the amount of damage will change as well. At level 0, it'll deal 1 damage.