Popokarimu (Labyrinth)

Chapter: 4-1 · Caves, Ancient Village and Labyrinth
Where: The Labyrinth: it flies down through an opening in the ceiling when, after pulling the chains on the last (red) statue, you try to leave.

Weak point

The fleshy red underside of the tail; the armoured front deflects bullets. While it flies only tail hits count, and a strong one brings it down.

The rematch, against an armoured Popokarimu. It is optional: you can run up the stairs and a QTE crushes it in the tunnel, but then there is no Soul Gem (₦10,000, its only source).

To kill it, stun it first and unload into the tail. Just before, a silver case holds the Grenade Launcher with 12 Explosive Rounds: on Normal its starting ammo is enough; on Veteran and Professional you need other weapons as well.

Reward

Soul Gem (₦10,000), only if you kill it. Escaping gives nothing.

Rushing straight to it clears the other enemies from the map: with Chapter Select it is a quick ₦10,000 farm.

Sources clash on shotguns: IGN recommends one, Fandom says it takes 40% less shotgun damage (unsourced). Both can be true: an upgraded M3 hits hard enough despite the penalty.

Step by step

Mine trick: before pulling the last statue's chains, plant a Proximity Bomb roughly in the middle of the room. It walks over it before attacking and, with upgraded weapons, dies during that first stun. There is a mine in a vase in the room next to the lower 4th statue.
No mine: a few direct Explosive Rounds from the Grenade Launcher or Hand Grenades stun it. Don't fire the launcher up close: the splash hurts you.
Once it flips, go for the tail: a well-upgraded M3 needs "a half-dozen shots" (IGN). The S&W M500 takes 5–6 shots to the head.
A Rocket Launcher to the head, without stunning it first, usually kills it outright. Flash Rounds take 12–13 direct hits.
To escape instead: run up the stairs and mash the QTE; fail it and you die.