Zurai said:
Tremorsense and Truesight are exceptions to the rules. I was going to say Blindsight as well, but actually that's not true: It specifically says "making Perception checks as normal", which means the Tarrasque also falls to a Cloak of Invisibility.
I'm not sure where you are quoting from, but DMG p. 67 is pretty clear that blindsight ignores invisibility.
Also, I see no indication that invisibility hides the physical effects of your attacks (such as bolts of energy from a wizard, or arrows from a ranger.) You can't be seen, but your attacks still can. Granted, there are no specific rules to determine the location of an archer from the angle of an arrow, but that is what the DM is for.
Lastly, a creature can physically search the battlefield by moving around. It cannot enter the invisiranger's square, so when it fails to move, it knows where the ranger is (or nearly so, depending on its size).
As for the comparison between the cloak and the scarab of invulnerability:
For solo adventuring, the cloak is much better. For a party, the scarab is. Rather than just removing one character from the target list (and providing a minor offensive advantage), the scarab actually lowers the total damage output of the bad guys, making it more likely that the part will win. Magic item levels, of course, are based on their usefulness to a party, not a single adventurer.
---
gnfnrf