Thanks!
The Fallen Five:
Siege could get ridiculous, but his slow start tended to give you some time to take him out. But absolutely, if you left him alone too long he got horrific.
In the wrong environment (like the Tomb of Anubis, which has lots of things that damage everyone), Revenant's environmental redirection is brutal.
Every fight we had ended up being a to the wire slugfest where at least 1 (usually 2 or three) heroes went down. Usually trickery was involved in surviving, like using Mist form to let the environment finish the villains off (at that point, the other three heroes were down, and the tomb of anubis was being hateful!)
The Child: I had a lot of fun writing her (it?). In practice, the Entanglements are kind of tricky, but you get used to them. I did a lot of playtesting, and while it helps to have heroes that can eliminate ongoings, you can do the job with tanks, redirection, mist form (or cocooning), etc. I really wanted her to be a villain that rewarded trickery and non-linear combat styles. Or waiting until the right moment for massive attacks!