local ItemID = 0
local Range = 5
local MobId

local Mob

function RegisterUnit(unit, event)
unit = Mob
end

RegisterUnitEvent(18, MobId, "RegisterUnit")

function Item_OnUse(item, event, player)
    if (player:GetTarget() == Mob) and (player:GetDistanceYards(Mob) <= Range) then
    else
    return 0 -- "Don't do anything"-mode
end
end

RegisterItemGossipEvent(ItemID, 1, "Item_OnUse")