the simple version
The adventurers reach a spot with some objects lying around, suddenly something attacks them one by one, in a single round. The four characters closest to the spot each take 1d4 damage at the head.
The referee then calls for initiative. Each player on its turn gets the same "You spot nothing", and on the opponent's turn, nothing happens. The combat ends, but the confusion should last.
the full version
The Affright is a poorly known beast somewhere between a cat and a rodent. It is excellent at fleeing, it can make up to four 5ft jumps in a round with a final 20ft jump to reach another cover. It's so fast that it's barely visible.
It jumps from snout to snout dealing light claw damage 1d4 on each of them. It doesn't aim at taking down the jumped creature, it just needs to sow confusion among its surrounders.
A character wearing a full helmet takes no damage but might get their helmet seriously misaligned.
The referee may grant a save to avoid the damage, but the confusion is a must.
The Affright is probably hiding not too far away. The adventurers may diagnose small claw wounds, but not much more. An affright needs a bit of rest between its frantic escapes. Too many such episodes and its heart might fail.
AC 1 , HD 1hp, Att 4 × bite (1d4), THAC0 19 ,
MV 40’ (4 × 5' + 20'), SV D14 W15 P16 B17 S18 (NH),
ML 2 (always fleeing though), AL Neutral, XP 10, NA 1 or 2, TT L