Randuins needs to be applied to Gankplank's barrels.
There's no reason that
shouldn't be applied to a skill that, not only ignores defense, but is an area damage that can also produce critical hits. Those barrels might as well be true damage the way they are set up and there's no way to counter them what so ever other than a lucky shot to hit it first. That crit reduction needs to be applied to his barrels as well when he's multi hitting 4 people for 1k+ each with 1 skill.
is a crit?

is 75% armor ignored