"make a script every time an player kills another player, their max health will increase 25 more and will add more 5 walkspeed and this sound id will play: "8863377426""

-- server script 
game.Players.PlayerAdded:Connect(function(player)
    player.CharacterAdded:Connect(function(character)
        local humanoid = character:WaitForChild("Humanoid")
        humanoid.Died:Connect(function()
            local killer = game.Players:GetPlayerFromCharacter(humanoid:FindFirstChild("creator.Value"))
            if killer then
                local killerCharacter = killer.Character
                if killerCharacter then
                    local killerHumanoid = killerCharacter:FindFirstChild("Humanoid")
                    if killerHumanoid then
                        killerHumanoid.MaxHealth = killerHumanoid.MaxHealth + 25
                        killerHumanoid.WalkSpeed = killerHumanoid.WalkSpeed + 5
                        local sound = Instance.new("Sound", killerCharacter)
                        sound.SoundId = "rbxassetid://8863377426"
                        sound:Play()
                    end
                end
            end
        end)
    end)
end)