Will-o'-wisp
About
A pale light out over the marsh, at about the height a lantern would be if somebody were carrying one, moving at about the speed a person walks. That is the entire trick and it has never needed a better one. It does not close, does not attack, and does not defend itself. It only stays a comfortable distance ahead, and waits at the edge of the firm ground, and lets the bog do the rest. It has all night.
Stats
Save Rolls
Traits
Special Attack
It has none. The wisp never attacks and cannot be made to. Follow the Light: 120 ft, save Wis Mind, fail save roll 1d4 psychic and the target moves toward the light on its next turn, which is toward standing water, sucking mud or a drop. Cooldown 1 round. Everything that then happens is the terrain's doing and should be resolved as terrain.
Special Defense
Nothing to Hit: it is a light. Melee cannot reach it, it takes half damage from everything, and it withdraws over water the moment it is threatened. Stand Still: a creature that stops moving and refuses to follow is in no danger whatsoever. The wisp will wait, patiently, and it is genuinely prepared to wait until dawn, and dawn is a long way off.