Whenever you see them on the map for example on stages 1.6, 2.1, 2.2 and 2.6. You have some bosses here that can be a legitimate pain in the ass But if you have a fire flask you can also 2-3 shot any boss. You start the duel,, throw the flask at them and when they run out of it to attack you, guard break them and throw them back in it which will around 90% of the time kill them. This saves quite a lot of time in these fights because all of the fights are pretty much RNG based because they mostly never guard in the same directions. For this I mean the actual class enemies and not the 2 bar HP enemies you meet a lot.