The Wayward Grave tunnels below the ground until it hears footsteps from above. It'll rush ahead below ground and pop up at the wayside, appearing as an open grave.
A successfull DC 16 perception check reveals that this is no ordinary grave, but in fact a monster waiting in ambush.
- •"It's your funeral".2d8+2.
The Wayward Grave extends it's pale pseudopods and grapples whoever is inspecting it. A successful DC10 Dex save escapes the grapple and halves the damage dealt.
- •"Rest in Pieces".
The Wayward Grave takes a grappled creature below ground. A creature below ground is suffocating and needs 2 successful DC 10 Might Checks to dig free. For each turn it stays below ground it takes one Wound.
Mimic? Ooze? Simply ignore graves next to the svalish road and you'll be fine.
If anything, these things are persistent and keep following and reappearing to their prey until they either enter a village or cross running water.