"Red-Icon" Beasts!

Hey there, anyone knows at which lvl the earliest red beasts can spawn? and WHICH one can spawn in the area? is there any informations?

I don't know exactly when these red beast start to spawn, but I've encountered my first one during act 2, in one of the first area. I guess they spawn at act 2 because that would let act 1 as a training act, to get a grip on the new mechanic with only common monsters and yellow beasts.

I also found my first - and only - one in act 2, in Chamber of sins lv1.