Since the comments inside the runs of the minigames are now disabled in Misc., I want to share a somewhat old comment of mine of the Waluigi minigame (some months ago):

I basically said that you can save up to 3 further seconds in there by performing a glitch. The glitch skips a green bob omb. It consists of throwing a bob omb at the Boss while it has started a "dropping bob-omb" animation.

Fail of 17 seconds (current WR is at 20 seconds):

Also, I think the minigame works like this: the Boss will drop 3 black bob ombs and then transition to a green bob omb, but every time you hit it, it will skip a bob omb in the cycle. So if you hit it before it drops a bob omb, it will skip to the next bob omb in the cycle. This is all intended behaviour.

(Black -> Black -> Black -> Green -> Repeat cycle)

What the glitch does is trick the Boss into skipping a green bob-omb while it drops a black bob-omb. It seems like the next bob-omb cycle starts even before the previous bob-omb in the queue has been summoned. So I trigger the Boss into skipping a green bob-omb in the cycle BEFORE it starts dropping a black bob-omb. As long as the dropping animation has started, even if there is no visible bob-omb in the screen, you can hit the Boss and skip a cycle. It can be seen between the seconds 17 to 20 in the video