Hello. I saw a button with a rat (the pet battle critter type icon) which I've never seen before. What is it? The new "snitch" version?

Ah yes, this new "snitch" will show you a breakdown of everyone in your group. If a person is below the required iLvL they will visually stand out in the list.

Allows you to easily see if someone is being carried and the group leader is not letting the rest of the group know.