Tremorsense

Tremorsense was a type of sense that a few species of monsters had. Monsters with such a sense could detect and precisely locate vibrations, including those of other creatures. Creatures with tremorsense had to be in contact with the source of the vibrations, thus, couldn't be used to detect flying or incorporeal creatures.

Creatures known to have tremorsense include:
 * Bulette
 * Black pudding
 * Cavelord
 * Purple worm
 * Earth elemental
 * Flail snail
 * Frost salamander

Spell
Some mages could cast the tremorsense spell, giving them temporary access to this sense.