This movie is OK

it's called being curt

ok so i think i'm understanding what you're trying to get at here now that you've changed things.
fearless and badass are separate, but perhaps related, things, fine. still wrong:

1. dry humor essentially defines this movie; it's filled with it.. possibly by every character at some point.
2. numerous time throughout, joey does or says something 'fearless' followed by active progression to either positive or mixed results, but with good effort by her. by this point we are already familiar what 'trying to look fearless' looks like and how that proceeds
3. this scene at issue is only time she ever appears to do so only to have immediate (and effortless by the antagonist) negative result
4. by trope trend, the last act in horror movies is a time when, after being beaten down repeatedly by the antagonist, the protagonist suddenly rises to the occasion, getting the upper hand or even outright defeating the antagonist - and often after verbalizing something 'badass'
5. after previously running scared for her life from him, literally trembling in fear while facing him down, and easily losing each of numerous physical conflicts with him, this was that obvious 'badass moment'. here she's meant to do that classic turnaround

it doesn't materialize of course. instead we enact point 3 above - getting situational subversion (immediately, not 2 seconds after the line in the next cut, part of point 1 above) - and do so in conflict with our expectation of points 2 and 5 above, and in direct contravention with point 4 above. altogether, these provide corroborative evidence for point 1 above, as humorous interpretation (like say monty python black knight 'it's just a flesh wound'). attentiveness, familiarity with horror tropes, and understanding comedic subtlety are required. so yes, it still went over your head

if you want to continue to claim you it actually played out as you predicted "the last two standing" go right ahead i guess. it's like wanting to claim the billion dollar powerball lottery prize by getting 2 of the 10 numbers. whatever, have at it

and again the 'good' analysis is nonsensical. yes it's already shown -etremely explicitly- by that point not to be an innocent child (and even showing the vampire to outright admitting to putting on the innocent act at one point). therefore whichever behavior it's meant to be exhibiting there, it's not to seem like an innocent child. now as a viewer if you have amnesia you might think that, but because you forgot by the end, does not mean the general audience is meant to. the promise gesture is merely the emotive vehicle through which joey can remember her promise and understand the vampire's intent. they both know it has nothing to do with actual innocence (we can assume joey does not have amnesia). the supposed conveyance of 'childlike innocence' -if there would be any- would be directed specifically at joey, presumably to help emotionally compel her as the vampire desperately needs immediate help. such would not be directed at the audience. the audience knows better. thats your fundamental mistake. so whatever 'mercy' the vampire shows it is for joey and joey alone (not for humanity for example), and it's transactional mercy, bypassing any requisite consideration of ethics; good/bad doesn't even enter the equation.. much less get presented

but if thats what you saw, then thats what you saw. what can i say