Bind Demon

You can bind

Fallen Shaman.

Once bound, they can

Revive both shamans or fallens.

You cannot use

Death Mark,

Engorge or other skills on those revived fallens or shamans. Similarly, you cannot target them with Unsummon.

If you leave the game, you lose the group of fallens, keeping only the "original" shaman.

Now you can have your own

Fallen party!

One point in this still is all you need.

You can get a physical immune mercenary when binding a stone-skinned demon with 50% base physical resists, you can get one with

Fanaticism (lvl 12), you can get one with

Conviction (lvl 12), or perhaps Might aura is your cup of tea? You can get a cursed demon on top of any aura who will cast

Amplify Damage on hit making your Echoing Strikes do double damage.

And any damage done to you will be partially transfered to it as well.

Consumed bound demon also provides a unique temporary buff, if you want to go that route.

Hephasto the Armorer gives you 20% phys damage resist and lvl 19

Holy Fire aura, as an example.
Urdar-type creature gives 105% enhanced damage.
Maw Fiend gives 47% poison resistance.

Yes, it is as OP as it sounds.

The Smith from Act 1 is also a great target early on once you have access to the skill