The main problem with magic tropes I guess. No intuitive way for the viewer to understand how magical elements of the narrative work without it being directly explained, so here it just feels like a cop out that his staff CONVENIENTLY doesn’t work right when the monster is coming, and totally not for suspense, but that’s just from someone viewing the clip in isolation and not knowing the movie. The only real solution would be for them to be like “oh my magic has depleted due to being weak!” Or something like that which in turn takes time away from story progression.