Today the Spotlight shines in a new direction. A revised direction. A revised rules direction. We begin with a familiar face (from three days ago) done up in his fancy new revised rules and sporting a revised role in your warband.
I chose the Guardian Mummy to start with because I found him an interesting example of a creature who gained a new play style since getting his new stat card. As I said in the first Spotlight on him, Guardian Mummy 1.0 seems designed to get in one solid hit against your opponent's main threat, then leave his horrible, ancient curse to do its work by weakening the target for his allies. The new Mummy prefers to get in one solid Rotting Claw attack, then shift away one square and let Fear's Dark Shadow pin the target in place. While this Mummy certainly wouldn't mind if some ally wanted to rain destruction down on a Rotting Claw victim, he really doesn't need the help of anyone except his own ancient curse to kill his enemies.
It's hard to overestimate the value of Fear's Dark Shadow. While it's contingent on the victim failing the saving throw against ongoing necrotic damage, the victim doesn't even get to roll that save until the end of its next turn. That gives you a free pass for one activation when you know that whatever that creature does, it won't be moving. In a game that's (still) all about positioning and movement, I don't need to say that this is like a pie filled with cake.
Another difference worth noting is that the new GM is both more and less durable than its predecessor. Being undead doesn't come with a huge list of immunities any more, but it still has a healthy set of resistances and Immune Poison. This latter ability is really excellent right now, because Desert of Desolation alone includes no fewer than 11 poisonous critters. What's more, the Mummy's Double Damage from Fire has been commuted down to a mere Vulnerable Fire 5, so those 65 hit points should go pretty far.
Obviously you could benefit from other sources of ongoing necrotic damage, such as the Babau and ... extra Guardian Mummies. While this will probably change as more sets come out, right now these guys are it.
The Drow Spider Priestess has a Champion Power that can force enemies to lose more saves against ongoing damage. More failed saves means more paralyzed enemies.
Your guess is as good as mine. Right now, there aren't any Epic-only creatures, so we don't really know how they'll change the landscape of Epic play. If you want to throw together 500-point warbands under the new rules, you'll just be up against more of the same types of creatures, in which case the Mummy will be roughly the same value for you as he would be at 200.