FPzero posted:

When you hit an enemy with the item it's weak to while that prompt is on screen, the attack they do next, usually signaled with blue particle effects, will not hurt you and will also suck in enemies while also exposing their weak point gauge. The idea is to hit them with that, close the distance while they're hurting the other enemies, then deplete the WPG and get the whole group at once.

I find it's usually not worth it to do the item weak points for anything that has Bombs because you actually have to line up the bomb throw arc and moblins never seem to be vulnerable long enough. I also skip it with boomerang-weak enemies because stalmasters and darknuts often do attacks that leave their WPG exposed. For the rest though, it's a good thing to attempt, especially against gibdos and redeads.