Nuclear Beasts

The Demon Hordes

There are at least six different "factions" involved in the Endless War, tearing up the realms. When a particular realm becomes "open" to inter-realm transport, it tends to get attacked by at least one faction... and often several of them. The relationship between the realms is complicated and obscure, making it almost impossible to predict when a realm will be open to transit, but you can scan for currently open realms.

• The Ravagers and the other Ravagers: believed to be the oldest force, these creatures are basically big, armored wolf-things that can teleport about by tearing holes in the dimensional barriers around them. Generally, a "scout" will arrive in a plane on its own, looking for prey. If it finds small creatures that it can handle itself, it eats them and keeps looking. If it finds more prey than it can handle, though, it will signal its bretheren. Then the entire pack teleports in and attacks en masse. If there's more prey than a single pack can handle, they send out a wider call and dozens of packs arrive. No one knows how many Ravagers there are in total. There are at least two separate groups (which are hard for outsiders to tell apart) because people have seen different groups of Ravagers fighting each other over spoils.
• Fiends: most of them are red-skinned humanoids with digitigrade legs, long tails with barbed ends and horns on their heads. It's said that they were once satyrs in the service of the Lords of Light, but their goddess was kicked out and turned them into a monstrous legion. Fiends who prove themselves worthy get enormous bat wings grafted onto their bodies so that they can fly. There are a wide variety of types, though, so not all Fiends look like the leaders and they use a lot of slaves as cannon fodder. Fiends are vicious and hateful but reserve their greatest rage for the Brutes.
• Brutes: humanoid warriors who have been practically welded into their ornate battle armor. The Brutes are smaller in number than the other forces, but make up for it with cold, dispassionate and practical strategies, good teamwork and a lot of military discipline. They live to expand their lord's empire and shun all human emotion besides a love of battle. It's believed that the Brutes were once in the service of the Fiends but broke away to establish their own empire. The two groups loathe each other above all others.
• The Lords of Light: a pantheon of gods that rules a tightly aligned cluster of realms that they call the Upper Realms. The Armies of Light not only defend their realms, they are known for interfering with the attacks of the other forces. Unfortunately, the gods' defenses depend heavily on conscripts bound with magical geases. So if they show up and "rescue" your town from an attack, they'll generally also seize everyone who looks like they might make a good slave... many of whom will find themselves brainwashed into serving as footsoldiers in the Armies of Light and helping to enslave other folks.
• Devourers: the most mysterious of the lot. Devourers don't even seem to have bodies. They infiltrate a realm subtly, slowly leeching the life out of it. Weak willed people tend to get possessed by them and corpses will often become reanimated. Plants wither and die. Even dead wood burns only fitfully. In the end, the devourers leave only a crumbling husk behind. Because they enter realms more slowly and subtly than the others, they cause the least overt destruction and the fewest rifts. It's possible to drive devourers away by destroying all off the people that they've possessed. Burning the materials that they've been leeching off of is a good idea, too. If their foothold in a realm is lost, the devourers will be drawn back to wherever they come from. While normally Devourers restrict themselves to possessing bodies, at the peak of an infestation they've been known to create bodies out of whatever random material happens to be lying around... they usually consist of a lot of mouths and sticky tentacles for propulsion. These can be discorporated by sufficient physical harm and it takes a lot of energy to do this, so it's often a desperation manuever right before the Devourers lose their foothold entirely.