Monsters which "sense invisible" can tell where invisible opponents are, and have bonuses to perception in other cases.
Effects of monster sense_invisible:
- For anything that just checks you.visible_to(monster), it's as strong as see invisible.
- Monsters with “sense invisible” have a better chance of noticing stealthy players than those with “see invisible”.
- “sense invisible” has some effect on a monster guessing an invisible foe's position: Without, it guesses within radius 2 around itself, with within radius 3. This makes it easier to escape from non-sensing monsters, but apparently makes sensing monsters less likely to guess your position when you're close (within radius 2) of them.
- Slightly decreased stabbing chance.
- An effect on beam targeting fuzz.
- Note that friendly summons with sense invisible can't actually detect invisible monsters.