On damage

Czesc, napisalem taki skript:

on rightclick:
    if player's tool is stone sword named "&4&l✪ &c&lMagiczna Bron &4&l✪":
        set {czas.magbron} to difference between {uzycie.magbron} and now
        if {czas.magbron} is less than 3 seconds:
            set {_x} to "%difference between 3 seconds and {czas.magbron}%"
            replace "seconds" with "s" in {_x}
            replace "minutes" with "m" in {_x}
            replace "minute" with "m" in {_x}
            replace "and" with "i" in {_x}
            send "&8&l[&6&lULTRA&e&lPVP&8&l] &cMagiczna Bron mozesz uzyc ponownie za &b%{_x}%" to player
        else:
            set {uzycie.magbron} to now
            send "&8&l[&6&lULTRA&e&lPVP&8&l] &aUzyles Magiczna Bron!" to player
            shoot a wither skull at speed 1.5
            wait 0.5 seconds
            shoot a wither skull at speed 1.5
            wait 0.5 seconds
            shoot a wither skull at speed 1.5

i chce zeby po trafienu w gracza tym wither skullem to zeby gracz otrzymal efekt obumieranie 3 pomoze ktos?