I would put it at a 2. Consent is present, and, assuming that the ...tentacle monster is capable of rational thought approaching a person, then it's just like fucking an alien.
However, it would be between 3 and 4 based on a few modifiers -- if the monster is not sentient beyond a beast, then it would be considered something akin to bestiality, in which case I'd peg it at a 3. If this is true, and the person purposely put themselves into the position with the intent of satisfying a fantasy, it is 4. Similarly so, if it is sentient and the second part of the previous is true, then it could be considered a 3.
Intent and a number of modifiers would change things.
So, crossdressing might be a 1 on the scale, but crossdressing with the intent of being caught is a 2. Being MADE to crossdress against your will, regardless of you liking it or not, would be a 5, and further modifiers based on the intent of the person forcing you would also increase (or decrease) that end result, with a minimum of 5 due to the "force" aspect.