When fighting various bosses I've noticed that by damaging(?) certain bosses can be poise-broken: they collapse for a brief moment allowing for a critical hit (like a riposte without parrying).
It's unclear to me why exactly this happens. First I thought it was related to the weapon weight, as it only triggered with Ultra Greatswords, but later I also managed to trigger it with shorter/faster weapons. Is it perhaps related to doing a certain amount of damage within a certain amount of time?
The bosses on which I'm clearly able to break their poise without a parry:
- Nameless King (and his bird-dragon)
- Twin Princes
- Darkeater Midir