monster!): the more actions one side has, the stronger that side is going to be. Remember the key thing about monsters vs. An owlbear wouldn't last long by itself near a tribe of goblins, for example. It needs a reason for it having survived in the dangerous wilderness. I wouldn't say a standalone monster counts as a tribe, per se, but the standalone monster definitely has to be strong enough to fend off the other creatures in the area.Or a recent eclipse brought on by the LEB obsessed with darkening the sky (easy trope) has caused the local Church of Light to lose their faith and commit mass suicide. Or the yuan-ti of the nearby jungle have brought a disease like grayscale from Game of Thrones to the City of Threshenstar. Maybe the local hag has frightened the villagers of Hodunk Town so much that they now refuse to trade with anyone. The LEB could affect the area through Regional Effects as you mentioned, sure, but they can also have reaching economic, health, religious, political, and social effects, too.It all depends on what kind of game you want to run. On the flip side, the CR could be a simple 1, as per the Noble stat block-easy to kill, but her strengths are in coin, charm, and influence. Maybe he's the Lord of the Local Crime Syndicate™ and beating him means killing/bribing/imprisoning/driving away his loyal following. Bosses can be defeated in other ways than combat, so if you want the LEB to be a CR 15 Archmage, make it so. The CR of the Local Evil Boss can be whatever you want it to be.

The tribe could be somewhere such as a decaying swamp consisting of corporeal and spectral undead, such as the typical skeletons and zombies (CR 1/4), shadows (CR 1), spectres (CR ), wights (CR 3) and ghosts (CR 4).all of them led by a terrifying wraith (CR 5) or necromancer (CR 4–CR 7).

The mid-level monster tribe is something your party might encounter early on as a major threat to the land, but won't fight until about 4th or 5th level.

Orcs and bandits would absolutely fit that category and are staples of D&D games.

Anything that constitutes a “low-level” tribe is anything CR 2 and below, as recommended above.

The big tribe leader could be something like a goblin shaman ruling (CR 1) or a fat ogre (CR 2). You're gonna wanna look for cannon fodder mooks that range anywhere from CR 0 to CR 1/4, and you're gonna want lots of ’em dotted around. The monster tribe could consist of creatures such as gnolls, goblins, kobolds, bullywugs-but any bipedal/ humanoid creature works extremely well.

Instaling Monster Tribe