Planar Bestiary
Primogenitors are so rare that not much is known about them. In fact, across the entire cosmos, one could probably count on one hand the number of intelligent beings—and that includes gods—who know about primogenitors. Which makes understanding them difficult.
But if one were to meet a primogenitor, even unknowingly, one might be forgiven for mistaking these powerful beings as relatives of insects, given that their humanoid physiology seems mixed with that of a huge praying mantis.
As their name suggests, primogenitors are likely predecessors of creatures that exist today. But not through direct descent. If certain stories can be believed, primogenitors are creatures from a multiverse that predates our own. How and why a few survived the end of their own cycle of existence and now exist within ours is likely a different story for each primogenitor. Except for the handful rumored to be hidden away in fossil rubble floating at the edges of existence, or possibly compacted and petrified at the core of a dead, dimension-hopping moon called "the Planebreaker."
Motive: Survival, accumulating power
Environment: Any very secure location in the multiverse, usually with an entourage of powerful servitor celestials and/or fiends
Health: 50
Damage Inflicted: Moderate wound (5 points)
Armor: 4 (6 against nonmagical physical attacks)
Movement: Short; short when climbing
Modifications: Resists magic as level 10; Speed defense as level 7 due to huge size
Combat: A primogenitor can attack five times each round, four times with their spined legs and once with their bite. If the bite attack hits, the target takes damage and is grabbed by the primogenitor's mandibles until the target can successfully escape as their action. All a grabbed victim's physical tasks are hindered. If the primogenitor starts their turn with a victim grabbed, as their action they can bite off the victim's head if the victim fails a level 7 Might defense task.
When a primogenitor eats a creature's head, their magical digestive process (which takes a few rounds) grants them the knowledge of everything that the consumed creature knew, including spells.
Due to an aura of truth magic that always surrounds a primogenitor, creatures within short range can only tell a lie if they succeed at a level 7 Intellect defense task.
A primogenitor can cast numerous arcane spells, with powerful options for attacks, defense, transportation, illusion, and divination.
Primogenitors can see in darkness, as well as see hidden or invisible creatures at long range.
Interaction: Primogenitors are very old and have had centuries to learn various languages (mainly by eating the heads of foes). They are aware of their age, power, and status, and do not tolerate insults, rudeness, or evasiveness (including attempts to evade their magical truth ability). With vast resources at their disposal, they are likely to be generous with lesser beings who perform a useful task or service.
Use: The supposed head of a criminal organization is secretly taking orders from an ancient, powerful, knowledgeable, inhuman thing.
Loot: A primogenitor usually has several useful cyphers and a few artifacts, possibly including a ray emitter (mind disrupting) ring, a ray emitter (numbing) ring, a rejuvenator necklace, and perhaps an artifact that transfers a memory from the bearer to a willing target (level 9; depletion: 1 in 1d20).
GM Intrusion: The primogenitor immediately makes two additional attacks or (if they aren't grabbing a character) an additional bite attack, even though it's not their turn.
GM Intrusion: The primogenitor immediately casts a spell, even though it's not their turn.