Why the fondness for Undead-heavy campaigns?

[Endarire]

Greetings, all!

I've noticed various posters mention about Undead-heavy campaigns more than any other creature type, though Humanoid-heavy (and often Human-heavy) campaigns have also been common. I'm even in an Undead-campaign on Sundays, and, in another campaign that ended about a decade ago with me as primary GM, somehow turned a campaign world that was not originally so Undead-heavy into an Undead-heavy campaign.

Maybe this fondness for the Undead is because of real life beliefs about life and death, a prevalance of Undead as enemies in other media (like Zombies!), and lots of Undead-bolstering and -fighting abilities in 3.5.

Interestingly, I've not seen anyone report about being in an Animal-heavy campaign, a Construct-heavy campaign, an Elemental-heavy campaign, nor a Plant-heavy campaign.

Thus, why the fondness for Undead-heavy campaigns?

[Eldariel]

It seems quite natural: undead are probably the most commonly present creature type and one that's directly tied to evil magic and thus most kinds of villains. It's very easy to produce various kinds of Undead with relatively low levels of magic and they're quite efficient. Also, many of the most iconic creatures in the game such as Liches and Vampires are not only Undead, but Undead Templates that can be applied to any creature and class. Indeed, the number of Undead Templates is probably the #1 reason; you have basically dozens of easy options to make an Undead version of any creature in the game. The other is incorporeality; very few things are as fear-inducing as horrors not quite in any world floating through walls and rending the soul. And most incorporeals are Undead.

In general, far as ties to real world beliefs go, undead are probably the most common example of supernatural things in contemporary media, next perhaps only to what D&D would classify as outsiders. Media does influence how we play, but the system plays its part too. There's a lot of support for Undead; even a major class feature of a major class that exists for the sole purpose of destroying them. And they are essentially eternal and easily also inhabit the typical forsaken dungeons players traverse, not to mention evil temples basically have no reason not to use them (since all normal Evil Clerics have access to Desecrate/Animate Dead and Rebuke Undead). And every faction has their Clerics so all evil factions also have their Undead. Not to even mention Zombie Dragons and the like. They're even PCable in Necropolitans.

[VoxRationis]

You also tend to notice undead-centric campaigns a lot more, because their blanket immunities make everyone go "What if we tried this—no, wait, undead." Your rogue can't sneak attack, your enchanter can't enchant, your ranger can't use wild empathy, your fighter just gets disappointed whenever a critical threat comes up... Undead are a pain to fight.

[Yahzi]

Thus, why the fondness for Undead-heavy campaigns?
In this modern age, many players are a bit uncomfortable with murdering sentient beings and taking their stuff solely because those beings are green-skinned, or speak a different language, or live in a different town. Kids these days! Whatcha gonna do?

But Undead? They're already dead! They're supposed to be dead! So you can bash them without any moral qualms.

[bahamut920]

Because the necromancer and his zombie minions and the vampire lord are iconic villains rooted in the public subconscious. Like the dragon perched atop his hoard of gold, virgin princess sacrifice tied to a stake nearby - or the hordes of Hell poised to destroy all that is good and holy - the undead are a threat everyone can easily imagine and frequently evoke a visceral reaction in the players.

Although I've personally only played in a couple of undead-heavy campaigns myself. The usual DMs of one of my two usual gaming groups tend to favor outsiders as enemies, especially at higher levels, and the usual DM of the other group favors humanoid opponents, usually with class levels.

[Fizban]

Undead are just easier, the next most obvious would be evil outsiders but they've got strings attached. Demons and Devils are supposed to be intelligent, scheming schemes instead of just fighting to the death, and often having a fistful of tactical abilities that must be used effectively (including the ability to just escape, forcing the group to replay the same fight again later)- but not so effectively that your players can't keep up. Even with the fiendish codicies it's hard to figure out their heirarchies well enough to be sure you're doing them "right," and they're supposed to be parts of big monolothic planar goings on.

Most undead are simple. They're often of middling or no intelligence, slaves to an unholy hunger, or seriously constrained by sunlight or other boundaries. They can exist in a place for no other reason than because someone died there who knows how long ago, or created deliberately. Their default assumption is attack until destroyed, and they can't usually just teleport away. No moral quandaries, clear, present, and surmountable threats.

Further, the bag of immunities mean fewer possible status problems for the DM to track and no problems with first round crit-death, their hp is never so high you have to do the math to be sure the PCs can kill it, and they often have attacks or abilities that will feel like significant damage after even a single hit. In addition to being an easy choice narratively, they're reliable mechanically.

An animal heavy campaign doesn't make sense: animals don't attack people constantly, so an "animal" campaign is actually a "druid" campaign with animals instead of undead. Constructs are usually too simple and difficult to justify in large numbers (though Maugs, being intelligent and reproducing, are an exception). Elementals are lacking in a number of CR bands and just don't "pop," anything interesting enough to be a focus is almost certainly an outsider rather than an actual elemental. Plants are also lacking in many CR bands, and there's only one real race of intelligent plant creatures: Myconids are underpowered for their low CRs, and their society gives them little reason to mess with anyone or have heroic/villainous individuals.

[Grod_The_Giant]

It's an easy thing to build a campaign theme around. The thematics and creepiness write themselves, and-- perhaps most importantly-- there are hundreds of published Undead creatures out there, with a wide range of unique abilities. You can throw multiple undead encounters at a group without repeating yourself or needing to write your own NPCs, in a way that's hard to do with most other creature types.

[Psyren]

Animal opponents aren't as satisfying to overcome because they lack agency/malice, and the other types you mentioned have all kinds of rules baggage associated. Undead make very satisfying punching bags at every CR; they can fit comfortably into both the mook and mastermind ends of the evil spectrum, and they can be used in both simple and complex narratives.

The same is true of Outsiders, but Outsiders have the unique problem that you have to always explain how they got there. A village overrun with zombies or wights might be uncommon, but it's plausible enough not to question too much. Overrun the same village with demons however and there usually has to be an overarching "reason."