A Deadlands: Hell on Earth Adventure by T. Jordan "Greywolf" Peacock
If the Posse arrives stealthily, they should have plenty of opportunity to get a look at the base before action occurs. If they acquired the APC and just drive it right up without thinking to stop and scout things out first, then things are going to get ugly quickly.
Initially, the Overlord's base has a crowd of thugs and hangers-on eagerly awaiting bloodshed in the arena. The majority of them, however, are likely to just scramble for safety if a fight breaks out, and a good number of the rest are quite soused anyway from all the partying on the Overlord's birthday. For statistics on the regular thugs, use the generic Raider profile from the rulesbook. Statistics for Warmongers and the S-Mart Overlord himself can be found in the Wasted West book.
The street running up to the front of the S-Mart Overlord's base is blocked off with barricades and sandbags, and a gun emplacement. The gun is on a heavy tripod, and can't really be moved from its current position. It takes one action to rotate the gun around to point in a new direction. (The ammunition box is mounted atop the gun itself, so actually the gun can be turned around all the way. Bad planning on the part of the bad guys, but we need that sort of incompetency to give the heroes a fighting chance.) Currently, it's covering the intersection, and is manned by two thugs. (If one gets shot, the other will most certainly take over and use the gun to return the favor.) The gun can only cover the street, the intersection, and be used to pick off a few positions overlooking the street (such as guard towers). If the Posse should manage to get control of it, other thugs are going to have the sense to get out of the line of fire.
The gun fires several bullets at once, but to save on the die-rolling exercises, several shots are treated as a single attack. The artillery skill is required to properly use the gun. shootin' may be used as a substitute skill, at -4. Treat the gun as having a Speed of 1, ROF of 1, "unlimited" ammunition (for the purpose of the scenario), damage of 4d12, with +4 to hit. (In short, if it hits something soft and squishy, it dies.)
If anyone using the gun does not have artillery, and rolls a Botch, the gun jams and is unusable until someone can spend 10 minutes of tinkerin' against a TN of 7 to get it operating again. The gun itself is a result of a bit of tinkerin', and if it gets hit with any sort of explosion, its ammunition hopper will explode for 6d6 damage, burst radius of 5 (same as a doom barrel). Of course, this will render the gun useless.
The exact number of defenders and their positions depends on the Marshal's best estimate of what's a fair opposition for the Posse. If you have an especially small Posse, that doesn't mean that they get to go up against just four or five guards, though. That just means that the Posse is going to be forced to try something other than just charging in, guns blazing. If they do that, let them die. The S-Mart Overlord wouldn't stay the "Overlord" for very long, if the average group of do-gooders can defeat him with a frontal assault at his home base.
Attempts on the part of the Posse to plan things out should be rewarded -- It's just that if they spend too much time planning and observing, they'll have fewer prisoners left alive to rescue. If the Posse does anything to cause the guards to sound the alarm, then any posted guards will be at least doubled -- if the Posse is careless, alerts the guards, and then falls back and doesn't carry on through to perform a rescue, they'll pretty much kill their chances of rescuing the prisoners without significant sacrifice ... or a really gutsy plan.
One approach would be for someone to scout out the area. The Junker's rocket pack may give mobility, but it doesn't give stealth, and if she shoots over the compound, she might get a pretty good idea where everything is, but she'll also alert the guards in the process. The Syker would be ideal for this. The Witch might be able to talk her way around, too.
One important note is that this is not a professional, military organization. It's a bunch of moderately well-armed thugs milling about, warning off potential trouble-makers largely just because of their number and the reputation of the Overlord. They have a few basics of organization -- watchmen posted at high locations, and alarms they can sound if they sense trouble -- but anyone who seriously wishes to infiltrate the place and has a modicum of covert skills can do so. The truth of the matter is that the Overlord himself has no concern of being assassinated, since he can't be. Most of the serious guarding is focused on ammunition stores, food stores and other valuable caches ... but these are not things that the Posse is after, per se. The guards are more prepared for straight-forward assaults from road gangs or mutants.
It's even possible to get around without having to be overly sneaky. The thugs have no uniform, and there are enough of them that any one punk doesn't know every other one. With a modicum of disguise or down-dressing, most members of the Posse could mill about without too much trouble. The only "uniform" is that all servants of the S-Mart Overlord wear S-Mart ID badges, S-Mart t-shirts or caps, or else they have "S-Mart" branded onto their skin somewhere conspicuous. A "uniform" can be easily acquired by mugging a punk or thug who's wandered off too far from the main group, or else by grabbing a marker and hastily scribbling "S-Mart" on one's forehead, and hoping that it will pass for a tattoo. There are "punks" of both genders, so the Witch and Junker won't have any harder time fitting in.
The Cyborg and Wolfling would require heroic efforts to disguise themselves, since they stand out so much that anyone working there can be certain he would have seen them before if they belonged there. The Doomsayer would need to swap off his robes for "civilian garb", the Law Dog would need to hide his badge, the Toxic Shaman would need to adjust his costume a bit, the Junker would need to stash the rocket pack somewhere (lest anyone ask questions), the Syker might want to cover his forehead with a cap, but he could always use Skinwalker.
The Soldier will look too conspicuous if he's walking around with a grenade launcher -- only a few people get trusted with something that potent, and he's not likely to pass for a familiar face -- but he can pass for yet another scavvie warrior if he borrows a few scraps from a defeated guard and swaps things around so his uniform doesn't look so, well, uniform, and more like something that he scavenged a bit of, here and there.
The Anti-Templar would look awfully conspicuous in his full suit of plate armor -- he might need to "dress down" a bit, at the expensive of his armor protection, or else do something like throw a scrappy-looking "cloak" over his armor, and carry his helmet around rather than wearing it. The Witch and Pit Fighter have no "uniform", per se, and would fit in just fine, provided they can grab badges.
Also, don't forget that the Witch can talk to animals. She could conceivably find some critter roaming about (There are plenty -- If she bothers to ask, she can easily find a crow or an alley cat, or maybe she befriended a giant rat from earlier) and bribe it to do some spying for her. The downside of this is that the creature can only report what it knows. It can let her know how many people are in an area, and it might even be able to discern who are dangerous types and who are the prisoners ... but it wouldn't be able to tell the Witch detailed information that would only have meaning to a human observer.
Then, there's always the power of interrogation. If the Posse catches some unwary thug wandering off too far, they could waylay him, and either threaten or bribe out of him some information on where the prisoners are being kept, and so forth. The S-Mart Overlord has not instilled a great loyalty in his minions, so this shouldn't be especially difficult. (In fact, they sometimes accost each other.)
The Syker's Skinwalker and Mindwipe powers provide lots of opportunities for mayhem. Not only can he sneak around and pick locks to doors, providing the Posse with a back entrance, but he could conceivably start fights between guards, or get them to leave their posts.
The Junker, Cyborg and Toxic Shaman can cause trouble with electronics in various ways. They could disable the alarms (buying the Posse a little more time if they attack before reinforcements arrive), disable mechanical doors, and so forth.
Don't forget - Although certain members of the Posse have a great deal more in the way of powers to use to come up with creative ways of dealing with the problems, anybody in the group may be able to come up with useful ideas -- even Antagon the not-so-bright pit fighter. Even if a clever idea doesn't work out, it may be a good idea to still reward such things with a white chip at the very least just to encourage player participation and teamwork.
Also, try to facilitate bright ideas. An inventory has not been presented of every single object the Posse might be able to find if they look about.
Another approach could be for the Posse to just walk on up, without bothering with sneaking or disguises. The S-Mart Overlord's base isn't on "alert", and the Posse doesn't necessarily represent an opposing force. (The Law Dog might be conspicuous, though.) If the Posse marches right up to the front door, they may get hassled by some thugs, and a fist-fight might even break out between some of the thugs and the Posse, while others hang back and just watch.
If the Posse doesn't end up bringing in the "audience" into the fight as well by lobbing some shots their direction, and they manage to hold their own, they may well earn the right to move on, simply because of that fact. If someone is foolhardy to walk in through the front door of the complex, he'll get the surprise of having the floor drop out from underneath him and getting dumped into a fighting pit with a large monster to deal with (in addition to damage from the fall).
If he fights his way through, he may earn the respect of the Overlord and the accolades of the punks. (Yay.) He would also have the opportunity, if he cares to, to challenge the S-Mart Overlord himself to a one-on-one duel. The S-Mart Overlord, unless he is otherwise occupied, cannot refuse such a challenge ... and it's the only way to defeat him. (See the Wasted West rules for further details.) If someone should actually defeat the S-Mart Overlord, his followers will break into chaos, as some of them run like crazy, some loot, and some of them try vainly to keep things under control. It'd be awfully easy for the Posse to slip off unnoticed (though whoever is stuck in the fighting pit could probably use a hand out). If the Posse makes a move to secure the prisoners in the chaos, they've pretty much got it made.
Initially, there are five prisoners being kept in a building across the street from the S-Mart Overlord's base. Once it's sundown, one will be taken over to the arena at a rate of one every two hours. Unless the Posse is actually watching the combat (in which case the Marshal might as well play it out), each prisoner will last a half hour -- by simply running around and trying not to get hurt, if nothing else. The prisoners are being pitted against a Wendigo (statistics are in Wasted West) that the S-Mart Overlord purchased from some adventurers who had ventured far into the northern part of the country.
Assume that the prisoners all have Traits of 2d6, and 2d6 in relevant Aptitudes, including sneak, climbin', fightin': brawlin', knife, shootin': pistol, throwin': unbalanced, dodge, and survival: urban. They aren't superheroes by any means, but they aren't totally incompetent -- or else this would be as much fun for the S-Mart Overlord as watching fluffy little bunnies being fed to the Wendigo. (Hmm. On second thought, he just might enjoy that.)
If the Posse manages to free several prisoners, and they aren't yet in the clear, just so the Marshal doesn't have that many more NPCs to keep track of, it might be an idea to assign control of the ex-prisoner NPCs to whichever Posse member(s) are guiding them out of the compound. For simplicity, and to represent that the prisoners are benefiting from (or at least depending on) the leadership of the Posse, don't roll Quickness separate for the prisoners in this case -- Any prisoner in the care of a member of the Posse will act on the same action cards that the Posse member does. The prisoners are primarily interested in getting out with their hides intact, but they are level-headed enough to be willing to fight, if given a weapon to use.