When I fight the first boss, Kayran (difficulty: Dark, version: 3.3.3.1, no mods), I attack the tentacles but they don't get cut. Simply theThe life of the monster goes down a bit with each attack until disappointingly with the successive attack the bar returns full or almost full, in an infinite cycle. Nothing else happens.
PS:How can I will answer my own question in 8 hours...defeat Kayran?