If I use a flashlight to investigate a location with a shroud of 2, thus bringing it down to 0, is it possible to fail that check? If I have an intellect of 2 and draw a -4, which brings my intellect down to 0, do I still pass since I've met the difficulty of the check? What if I draw the auto fail tentacles? Auto fail treats your skill as if it is 0, so I've still met the difficulty of 0, which should be a pass.

Seems to me if you can modify a difficulty check to 0, then it's an auto pass. Of course you may still suffer some negative consequence from drawing some certain tokens but, the test would still be successful no matter what you draw. Sound about right?

You still fail on an auto-fail.

You are academically correct, but it is a mathematically-verified fact that if you reduce a skill check's difficulty down to zero, you have a 100% chance of drawing the Tentacle Token, which is naturally the only way to fail such a test.

The tentacle always makes you fail (this is also true of any card effect that says an investigator automatically fails a skill test). The rule about setting the total value to 0 is in addition to that, for when the margin of failure matters ("for each point you fail by" stuff).

Got it . Curse you tentacle token!