MiniShadowDemonLargeLv 82

Infernal Nightmare

≈40per kill

fresh monster

≈67per kill

near level 10

Where to find Infernal Nightmare

If you have never hunted itIt pays orders of magnitude more than a normal monster: ≈40 research per kill at level 0, rising to ≈67 near level 10 — unlike a normal monster, the rate does not fall as the level goes up.
If it is the only bottleneck of your lineEvery kill is worth 2 to 8 times what its own research pays, because it is unlocking the bonus for all five.
If it is ahead of the other fourHunting it unlocks nothing — and a mini shows up rarely and drags the map’s pace, so the time is worth spending where it moves a bonus.
If the line is incompleteIt pays no bonus at all — the kill is worth only the individual research.