@Aegeri- I think you overestimate that particular party's ability to deal damage. Yes, there are a lot of stun/daze/immobilize effects out there for a paragon party, but they do run out.
That is true, but many of these are encounter powers and that works well also. Like, between those 5 characters you listed I can make a party composition out of them that will easily kill the purple worm. Even in the extension where the party is immensely badly injured and almost out of resources I think I could still manage with your party composition to win easily. It all depends on if you agree to let me have the wizard with Winged Horde.
If the wizard in the party has winged horde that's the end of the Purple Worm

To be honest winged horde is still one of the best at-wills in the game for a wizard - one of the things it does best is really work over monsters that rely on grabs.
And unless your party is willing to chew through all their dailies for a standard encounter, the big bag o' hit points that a MM1 solo is will still be around.
This goes back to the "grind" argument. They grind out combats - they do not make them entertaining or fun.
It only takes one swallow to scare the PC's, and while 2d8+7 damage isn't much for a Fighter, it can be quite a bit for a Wizard.
A level 16 wizard with 8 starting con will have (4*15+9 = 69 HP). 2d8+7 still takes more than a significant amount of rounds to get him to bloodied - at least two. Given that the squishy wizard can often teleport per encounter (couple of times often), the Purple worm isn't presenting any significant threat unless he's pre-wounded for at least two rounds. Or the DM gives it a surprise round (as is the case below).
Not to mention few clerics will bother healing until someone is bloodied, and with this creature, a softer character will go from unbloodied to swallowed in a flash.
Assuming it has the actions to swallow and can even grab a PC to begin with. If the wizard has Winged Horde you might as well forget about the Purple Worm doing anything (As you can't grab when you can't make OAs).
It's designed to be interesting and fun, which these monsters can easily be.
I disagree it will be either. By your own admission in the post you concede the only thing the creature can do is grind down HP (as that is, in a nutshell what MM solos are good at). Essentially it hopes not to get affected by a large number of conditions that will instantly prevent it doing anything. For example, if it gets immobilized and the party just walks out of reach the worm is instantly doomed to doing nothing.
You either get obscenely lucky with dice rolls or you die without doing anything significant. That's not a good monster.
All you wanted was a decent encounter, and there you have it.
I disagree, because I cannot see it competently challenging that party composition at all. Your encounter design is fine but it doesn't actually help the purple worm any for the reasons I gave, so you haven't succeeded
The Little Raven said:
They had been adventuring through the desert and had a run-in with a caravan of tiefling diabolists, got attacked by a group of desert bandits, wandered through a sandstorm and was ambushed by the purple worm. The fighter was down to 1 healing surge because of the failures during the sandstorm and the healing during the fights (and between). He was about 20 above bloodied and was waiting for a chance to get hit by a Healing Word or something to get more benefit from his remaining surge, but the rest of the party was at or within 5 hit points of full.
That was a very poor mistake on their part, but getting very lucky with a monster does not make it effective.
On the surprise round it got, the worm bit the fighter, grabbed him, and bloodied him with max damage. It won initiative, and swallowed the fighter immediately. It spent an AP and bit the cleric, grabbing him (for max damage agaim).
So an obscenely lucky set of circumstances against an immensely wounded party let it manage to actually do something? This isn't the most convincing scenario - especially as it relies purely on luck.
The wizard was almost entirely useless, as all of his remaining big guns were illusions.
So if he was an illusion wizard why didn't he have winged horde (unless it wasn't available), which would have instantly prevented the purple worm from being able to reliably grab any PC for the rest of the encounter? Unless of course he's a wizard who takes lots of daily illusion powers and then neglects the best powers for someone with illusions.
The ranger was out of dailies, but was pretty consistent with his other exploits. The avenger was moderately useless, because the player was rolling pretty poorly most of the fight.
So very lucky rolling on your part, poor rolling on the PCs part, plus you throwing a surprise round on them, they have barely any healing surges left, with a creature that is all HP/high defenses means that in a grindy encounter a grind based solo monster actually has a slim chance of doing something. I could have told you this
Of course if it hadn't been given a surprise round, hit, rolled maximum damage, got higher than every PC in the party in initiative, hit again and rolled maximum damage again I doubt this would have gone anywhere near the same. That's an obscenely lucky set of circumstances I must say, but it doesn't demonstrate this encounter works or makes the purple worm challenging.
Yeah, this was against a party that was already hurting a bit. However, even at max HP, the worm's double max damage could have bloodied the cleric immediately and the worm could have swallowed him before anyone could act. And that would mean no heals for the party until the thing is dead, which does change things.
So I can assume that the Cleric has only a maximum 82 HP (bloodied would be <46) HP. Assuming he has moderate con (starting con maybe 11?), he's got con 12 + (70/5) = 14th level? As the purple worm is 16th level, that's roughly a EL + 2 solo (minimum), with a surprise round, with most party resources exhausted, with soldier maths and lots of defenses/HP that's very little wonder they had a problem. Of course I am wondering what powers the party had, including dailies and similar.
In the end though you've actually proven my point (ironically) as technically this isn't actually a success for the purple worm. In reality that should have been a TPK immediately with that situation. It's only the fact the purple worm is so terrible that it couldn't actually manage to finish off such a party in an immensely weakened state, with literally the stars aligning
absolutely perfectly for it. Let's say we took another "early" solo and did the exact same encounter, replacing the worm with it.
It sounds like a good encounter and you picked the right monster: You picked the right monster because you took something that is absolutely terrible that WOULD work in that situation.
Zany logic I'm employing here isn't it? But let's put in another monster in this exact same situation shall we. If that had say been an elder brown dragon, which is a level 16 lurker the first round would probably have seen multiple PCs hit by its breath weapon (blocks line of sight). On its own turn it would have then used frightful presence, probably stunning a good chunk of the party and then APing for a dual claw attack (same damage as the worm, but he gets +3d6 damage due to having CA from breath weapons effect). Then he would have used sandcloud for an additional 2d6+4 damage.
So in the equivalent situation where the purple worm got lucky and managed to challenge the party, the Brown dragon would have done:
Surprise round; Breath weapon: 3d10+4 - assuming this is on the fighter or perhaps the whole party in a surprise round penalty box scenario (not unreasonable given your example). It blocks line of sight, so the dragon will get CA (as he'll be invisible to the PCs when attacking).
PCs within the sand cloud cannot see the dragon, so his attacks will gain CA against them - this means we're about to hit the ridiculous switch for damage.
First round: Dragon gets initiative (It has better init than the purple worm)
Standard: Dual claw: 2d6+7+3d6 damage x 2. If both hit the fighter will take roughly 10d6+14 damage.
Action Point: Frightful Presence: Most of the party is probably stunned (or a good chunk of it)
Move: Sandcloud, move through the PCs affected by the breath weapon. Deal a further
automatic 5d6+4 damage and blinded to every PC (as the combat advantage is worded when it deals damage, not when it hits with an attack and he certainly has combat advantage!). He can make a stealth check too while he's doing this to become hidden so the blinded and LoS blocked PCs have utterly no idea where he is.
Every PC takes 10 damage at the start of their turn, has no LoS due to the breath weapon and is blind.
So in that scenario, the purple worm that I decry as terribly designed gets to deal 23+23=46 damage in one round, in optimal conditions when you've stacked the deck absolutely in its favor.
When I do that for the Elder Brown Dragon in that same theoretical situation I get - optimally if I hit with all attacks (against the same PC) and taking an average damage:
4d10+15d6+22 damage in the surprise round + first round - before any PC has acted. That's an average of 96.5 points of damage. How many HP did your party have out of curiosity?
Against the whole party (on an individual basis, assuming attacks hit - which isn't likely to occur with every PC). I've done:
4d10+5d6+8 damage in the surprise round and first round - before any PC has acted. That's an average of 47.5 points of damage. Again, to every PC in the party before they've acted.
On top of all this I've likely stunned, probably outright killed someone and blinded the entire party. All without them taking an action and the dragon is hidden so they don't know where it is so they can't fight even if they didn't get stunned.
So... does my point about the Purple Worm stand
Like I don't bring this up to pooh pooh your example, but it does rapidly show the gulf in power adequately. That the purple worm is terrible enough not to lead to a TPK in a situation
made for it to do so proves my point. You're also a really good DM if you picked it especially because it wasn't very good for that purpose. Had you picked something else like my Elder Brown Dragon above, you just killed your party!
Edit: Look at those numbers, I mean wow. I don't even
need to roll max damage - just the
average in the same situation to outdo almost 3-4 entire rounds of purple worm damage in the same situation. If I roll a crit or two that just gets ridiculously sick.
Edit2: Another damage breakdown for the Elder Brown dragon, without using frightful presence and the interpretation that sand cloud will get damage added to it for CA from their CA feature. This time the dragon gets lucky in recharge rolls. I assume he rolls his breath weapon and sandform recharge rolls.
Surprise round: Use breath weapon, dealing 4d10+4 damage to all PCs.
First Round:
Move Action: Use sandcloud to blind all PCs, dealing 2d6+4 autodamage and blind to all PCs.
Standard Action: Breath weapon dealing 4d10+4+3d6 damage to all PCs.
Action Point: Dual Claw attack against Cleric - coup de grace twice if he's already down. Either another 4d6+14+6d6 damage, or alternatively 74 straight damage all the way to negative bloodied.
Overall damage (Single PC): 8d10+15d6+26 damage = 44+52.5+26 = 122.5 single target damage. I outdid my previous calculation here and I didn't use a somewhat dodgy rules interpretation about the sand cloud getting the bonus CA damage. This is more valid than my argument above because of that. Noting that I assume luck only in getting the recharge on both powers - not on hitting with every attack. As the dragon will be attacking the whole party most likely, he has the pick of the litter in terms of who to kill first in this scenario. Whoever is hit by both breath weapons or goes unconscious is effectively doomed in this hammering. Plus the dragon can just follow it up with frightful presence if he feels like it.
In the same time the purple worm did a whole 46 damage and swallowed a PC. Bear in mind that damage above is immensely optimal, assuming no misses and such. But also bear in mind that dragon is wasting the
entire party simultaneously. Also the dragon has completely crippled the entire party: Not just one member (Sand cloud has no roll to hit, there is no luck involved there!).
The point of this is, that if you use the example of a party being pre-wrecked before an encounter with a purple worm, how does it fare against a similar "era" solo (Draconomicon) in the same situation? The answer is pretty obvious. Now if the purple worm can't do what the elder brown dragon
trivially does in the same situation - I think that proves my argument.