Reactionist
A dumb term used by these guys. Reactionist are not to be confused with reactors for they are original. Reactionist are not original. In fact they're terrible.

Why are they terrible? Well here's what they do: they watch a video and they react to it. You may be saying to yourself "Well that doesn't sound too bad." Well here's the thing: they aren't even creative about it. No editing, no jokes, nothing. They play the video and its entirety and give the occasional "oh shit" or "dayum" while rambling on at the end.

You may be saying, "Well ok, that sounds bad, but it's not like their hurting anybody right?" Well here's the thing: THEY ARE.

Let's say a YouTuber made an animation and he/she uploaded it to YouTube. He/she worked really hard on it and they could really use the views for money. A reactionist uploads a reaction to it. Now an average viewer could stumble across the video but instead of watching the animator's version, the viewer watches the reactionist's video. The viewer doesn't watch the animator's version because he/she already watched the reactionist's version. The reactionist gets the money when it should be going to the animator's.

Again, there's a difference between a reactor and a reactionist. A reactor doesn't show the whole video.

Also don't believe it's helping a channel who wants advice. It's called a review.

In the end, reactionists are terrible people whose channels should be taken down. They're shitty videos for twats.
I uploaded a video but a reactionist got all the money.

Sucks.