Ooh, a lot of attention from Jormengand! Let's have a look.
Okay, I had to look this mechanic up, but... Holy crap. Holy honking crap. Whenever this creature attacks, defending player sacrifices N permanents. And that number is 7?!
I did a quick search, and of the handful of creatures that have Annihilator, the highest one has Annihilator 6, costs 15, and is a 15/15 Legendary Eldrazi with a boatload of abilities. Admittedly, having a sacrifice 7 permanents casting cost is a pretty big price tag, but still. This is kind of a big deal, and I love it.
Moving on.
Okay. So, quick recap, Stained Glass Demon is a 4UB 5/5 Demon with Flying, and when it comes into play, you exile all permanents and replace them with identical tokens. Hell's Hammer gives a creature Annihilator 7, meaning that when it attacks, the defender sacrifices 7 permanents.
The combination of the two does neither, which is really interesting. Steal every exiled permanent and take control of it, recycle non-permanents to your hand. It's clever and dangerous, and while it doesn't quite have the same "holy crap" factor as the Hammer, it does kind of make you a dangerous recycling machine.
Requires some strategy to use, but potentially devastating.
This is so interesting. For reference, Fel Bargain lets you search your deck for a card, then costs you 2 life thereafter. Great for a cheap way to grab the card you want, but costly in the long run. This one, similarly, is a potshot at the enemy and creatures - perfect against a critter deck - but costs you 2 life thereafter.
Both cards get a cheap, moderately useful effect right now, at the cost of a long-term recurring penalty unless you can get rid of them.
Basically, this offsets the recurring cost of its constituent cards by letting you enjoy their benefit over and over. While losing 4 life per round still hurts, you can offset it with the card of your choice from your deck and a quick potshot at all enemies and enemy creatures. It basically puts a time limit on the game, but it's potentially devastating if you need certain cards to win, or against a critter deck. Clever!