Pointed Discussion

I also think that it's not the cheapest artifact out there, but the effect is definitely useable since it does not require anything but tapping.
Like that you can save any x/2 creature wanted once and evetually trigger its cip/etb effect a second time.

And as Belz already said, this card does a great job in a deck running creatures that enter the battlefield with +1/+1 counters on them, since this means the -1/-1 counter gets negated by the +1/+1 counter, and if the creature has still one left, it can be saves with persist repeatedly.
Keep in mind that the returned card is treated as a completely new creature - that's why the cauldron didn't simply read "creatures you control gain persist until end of turn", since this would have meant an easy loop with accordant cards.

Acrbound and Simic creatures are such cards. Any guy with Modular/Graft 2 or more can be saved each turn.

Other usable creature with the Caudron are creatures with Amplify, Bloodthirst, most Clockwork creatures (although most of them are hardly playable in general), Phantom creatures and Spike creatures.

Further cards which will also provide some profitable effects are:
- Pentavus, Thopter Squadron, Triskelavus, Triskelion or Ulasht, the Hate Seed can be used for creating tokens and/or dealing damage.
- Sekki, Seasons' Guide, Petrified Wood-Kin, Karstoderm, Magmasaur (also with useful upkeep effect), Wiitigo and Stag Beetle provide good bodies
- Heartmender of course as already stated twice, Fertilid provides a Rampant Growth each turn, Stingmoggie a Demolish effect, Golgari Grave-Troll, Hunting Moa since it can save itself and put a +1/+1 counter on another creature when it leaves, Juniper Order Ranger will save any creature with persist while he is in play - you can create a saccing loop with him and a creature that inherently has persist btw, Kinsbaile Borderguard for Kithkin, Mighty Emergence for fatties, Oona's Blackguard for Rouges, Workhorse for creating mana, Rage Forger for Shamans, Sage of Fables for Wizardsand Sigil Captain for 1/1 creatures.

Oh, and you can get the cauldron effect once for two mana in instant form as well.

Lots of fun combos here.
With a dingus staff in play, and a mass kill spell (flamebreak, wrath of god, hurricane, etc) they take a lot of damage. Then they all come back, and everything with a toughness of one dies again for more damage.

Why in the world does this have such a bad rating? It's an extremely valuable artifact in a game full of removals. To break it down, yes its an expensive artifact, but no more so than it would cost your opponent to cast a wrath of god and it can be tapped the first turn you play it.. and as such it comes in at the perfect time, especially with mana accel. So, while it might be moderately mana expensive for an artifact, the anti removal your getting out of it is insane. Top that off with creatures that can remove their own counters, via quillspike, heartmender, diety of scars, or noxious hatchling, and you have persist creatures that can keep on persisting, turn after turn after turn. Once cauldron is on the field your creatures aren't getting removed unless they get exiled. It gets past the majority of anti removal spells in the game, and considering what a hefty amount of cheap removal spells are currently out there, it certainly doesn't hurt. Can also pair with cards that wouldn't normally be allowed to have persist such as creatures that do damage when they enter play, like allies, or flametongue kavu. Another combo is ooze garden, have several creatures gain persist, then all hit the graveyard at once for your ooze garden oozes giving you double the creatures.

Great card for slow formats like 2hg, 3hg, ffa or edh/commander.

It makes your guys leave-play and come-into-play abilities trigger twice. Witness regrowths you two cards, solemn rampant growths for two lands and draws you two more etcetc. Creatures that come into play with +1/+1 counters, like triskelion, spikes or graft creatures, can be persisted with this card any amount of times. Not to mention that your guys are harder to remove as well.

You can also use it on your opponents creatures when you have horobi in play or whatnot.

screws Doubling Season

Heartmender.

Well, Shadowmoor certainly wasn't a bad set, although I'm kinda biased since I was introduced to Magic with that set.

Cauldron of Souls works well with Heartmender, as was said before, and there are several ways to get rid of the counters as well. Considering the fact that the activation cost is a mere tap, it's really not that bad.

The Cauldron also works pretty well with the older Modular and Graft keywords.

Added: I recently constructed a deck with this and Cauldron Haze, using it to bring back creatures that can sacrifice themselves (all Wizards) and Sage of Fables to negate the -1/-1 counters to allow re-use.

Quickie combo with Infectious Host.

Throw this in an ally deck since the +1/+1 counters cancel out the other ones. And the nof course if more than one die at the same time, they can both trigger eachother's abilities. Good times! :D

maybe run with Ravenous Baloth, Wirewood Savage, and Aether Charge in Beast tribal for tons of fun?

Combos with Allies :)

You can make Jenara a fearsome general with this in play.

Wait... not only would this be really good with Soulshift, it would be incredibly thematic. Cauldron of SOULS! SOULshift! Woohooo!

ha this would be funny in my deck, oh also yay gravepact and 1/1s now my creatures get to die twice!

visiting this card for a second time I realized the potential of this card in my deck is beyond what I expected.

I was kinda naive back then...

my deck is based around about 3 things
1. come into play/go to the graveyard abilities.
2. gravepact/butcher of malakir/braids, cabal minion/stronghold assassing/sadistic glee.
3.recuring nightmare/hells caretaker/other reusable reanimation that preferebly but not neccessarily puts creatures directly into play.

@ infernox10: no, you cannot bring back tokens with persist. Tokens exiling when they leave play is a state based effect, it does not use the stack.

My favorite card to use with this?

Cowardice

No creatures on the field except yours.

this + Melira, Sylvok Outcast = free regeneration

This must be good with Graft creatures right?

Tap this with Kokusho, Melira, and a sac engine.

I'm wondering if I should use this in my Replica Deck...
Since I can effectively use it to double the amount of times I can use the replica

I'm gonna put it into my The Mimeoplasm EDH deck.

Crazy with Ghave, guru of spores. He just loses a +1 counter when he enters the battlefield, and you can just keep pumping out saporlings every turn.

Really just amazing with any EDH deck. It found a spot in my Kaalia of the vast deck even, getting around all the board wipes is an amazing ability. On top of it all this plays all the political games you need to play to get your deck around an awkward draw.

Sarkhan the Mad anyone?

This is amazing in a Simic deck. The -1/-1 counters will be negated, making it very hard to kill anything of yours. You also don't need to worry about your creatures running out of +1/+1 counters from overusing Graft, as your creatures will just come back again once they run out of counters.

However, people seem to forget that once the creature goes to the graveyard and then comes back it no longer has persist, it's treated as an entirely new creature.

Fun with Undying creatures, like Vorapede.

Wait, what?

PROTIP: Just alternate between Persisting it and Undying it.

If a creature has both Undying and Persist, it is unkillable. If only there were a way to get multiple uses out of this in one turn. Then you could sacrifice a creature any number of times all at once to multiple effects and abilities.
What about...
Have this in your graveyard, exile it onto Myr Welder, use Palladium Myr and two Myr Galvanizers to get an infinite untap (but not infinite mana) combo on the Myr Welder. You can use the welder (and by extension, Cauldron of Souls) any number of times per turn, on any number of creatures with Undying. Proceed to sacrifice them to anything and everything any number of times, setting off the desired number of death triggers and sacrificing abilities.

Invaluable cards would include: Bloodthrone Vampire, Rage Thrower, Falkenrath Noble, and whatever sac outlets you feel like feeding into. Butcher of Malakir can work too, if you feel like going overkill. I like Bloodthrone because she can block all day, and doesn't require any mana to pop a creature.
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EDIT:
Alternate combo!
This (Cauldron of Souls) on the field, Isochron Scepter imprinted with Undying Evil. Xenograft(myr) and March of the Machines down alongside.
Any mana-producing creature and an Alloy Myr.
Two Myr Galvanizers.

Any and all creatures you choose are undying and persistent any number of times a turn(barring Split-Second kill effects), you have infinite mana in all colors, any sac outlet has infinite fodder, abuse EtB effects to no end...

I believe this may be the most comprehensive infinite combo yet devised. Of course, when you add it all up, it requires a total mana investment of...
++++( or )*+++
A grand total of either (23)+ or (21)+
A steep price for nigh-omnipotence.

*For either a mana Myr, or Llanowar elves.

This with undying creatures makes a thing of beauty.

Also, are people forgetting that the rules say that +1/+1 counters never completely cancel out -1/-1 counters anymore. personally i think that it's kind of stupid, but i also liked mana burn. anyway, a lot of the proposed strategies for using this card in these comments are now obsolete (sadly)

What happens if a creature with undying gains persist?? And vice-versa..

Welp. Widespread destruction like Wrath of God is finally not Slivers' one uncounterable weakness.

Use with power conduit for repeated persist with just about any creature

Mikaeus, the Unhallowed. He makes a stupidly too good EDH general already. Get this on the board, and your creatures will never die. It's a more powerful combo than just using Avacyn, Angel of Hope because -1/-1 counters or "becoming -1/-1" until end of turn won't ruin your day either. Only being removed from the game or countered before entering the battlefield will do it completely. And in EDH, they can only run one Final Judgement. Bouncing will delay you, but not the biggest deal. Run some cards with Unearth if you're worried about being countered.

I have a friend who uses it in his Horobi, Death's Wail's EDH. It kills everything. XD

@Turtleknite: Actually, at least as of October 2012, they negate each other once more. From the compiled rules, element 123.1:

--If a permanent has both a +1/+1 counter and a -1/-1 counter on it, N +1/+1 and N -1/-1 counters
are removed from it as a state-based action, where N is the smaller of the number of +1/+1 and -1/-1
counters on it.

This makes me breathe a sigh of relief; the idea I had for a Commander Jenara deck relying on the interplay between graft (and other +1/+1 granters) and persist is still viable.

Mikaeus the unhallowed =)

Crazy card with evolve (esp. In EDH). Creatures come back, evolve back to the +1/+1 range, and suddenly are ready to persist again.

This card used to be kinda funky and cool, but now that undying and evolve are here, this thing has some many fun uses.

Combo with Novijen, Heart of Progress?

combos with murder when facing down a Phage the Untouchable

All I see is "the Black Cauldron" and the horned king standing over this.

I love this card and its little brother Cauldron Haze. I use them both in my Karador "sac for value" EDH deck because I have a lot of creatures with ETB and death triggers, and they let me sacrifice creatures without having to actually lose my creatures. I've done stupid stuff with them. One time, I did this:

1. During the end of the turn of the guy before me, cast Cauldron Haze targeting Solemn Simulacrum, giving it persist.

2. Cast Altar's Reap sacking Sad Robot, drawing a card, searching for a basic after he persisted back, and then drawing two more cards.

3. Draw for turn. Somewhere in the middle of all this card draw, I drew into Skullclamp.

4. Play Skullclamp and hook it up to my now 1/1 Sad Robot. Draw three more cards.

Another time, while I was fishbowling, I did this:

1. Hardcast Shriekmaw while I had this, Karador, Phyrexian Altar, and Grave Pact out. Blow up a creature.

2. Activate this, giving Shriekmaw persist.

3. Sac Shriekmaw to Altar for . forcing everyone to sac a creature. He persists back, blowing up another creature.

4. Sac Shriekmaw to Altar again for , forcing everyone to sac a creature.

5. Use the two to evoke Shriekmaw from the grave with my Karador play, blowing up another creature and then forcing everyone to sac a creature. (Yes, you can stack it such that your opponents can't just sac the creature targeted by Shriekmaw.)

In a four-player game, that one Shriekmaw would've taken out a dozen creatures.

Overall, I'd give this a 4/5. It's got a hefty cost, but that ability makes for some awesome utility.